Introduction: Insulating Curtains That Cut Heat Losses Through Windows by 50%

Picture of Insulating Curtains That Cut Heat Losses Through Windows by 50%

20 to 50% of all the energy that is used to heat up a typical home during the winter is lost through its windows. This wasted energy increases our heating bills as well as our carbon footprint, neither of which does anyone any good. With this in mind, we designed the Kume curtain: a simple and inexpensive do-it-yourself insulating curtain that can help us save money, keep our homes cozier and be kinder to the environment.

"Kume" in the language of the Mapuche people of Chile means "good." We feel that this name is well-deserved as the performance of these curtains is very "kume" indeed. The thermographic photograph shown above speaks for itself. It was taken early one winter morning and clearly shows that the window fitted with a Kume curtain is much cooler than the one fitted with a conventional decorative curtain - and is actually even cooler than the masonry wall. This can mean only one thing: instead of letting the heat seep out of the house, the Kume curtain keeps the heat in, where you need it.

The benefits offered by Kume curtains are as follows:

  1. They lower heat losses through windows by 50 to 70%, and improve comfort by eliminating cold spots and drafts in rooms. In the first test homes fitted with Kume curtains, heating fuel consumption dropped by 25%.
  2. They are inexpensive. The cost of the materials that are needed to make a Kume curtain typically ranges from US$ 1 to 1.5 per square foot.
  3. They are easy to make. Putting together a Kume curtain does not require great manual skills or much time. For example, assembling a 2x4 ft curtain takes less than two hours. The hardest part of making the curtains is cutting the panels straight and to size. If you use polar fleece for the panels, you don´t even need to hem the fabric, and the whole curtain can be assembled without a single stitch.

Step 1: What Is a Kume Curtain?

Picture of What Is a Kume Curtain?

It is a roll-up curtain that is composed of four distinct layers.

1) A front panel which acts as the first layer of insulation and seals the perimeter of the window opening when the curtain is closed.

2) A moisture barrier which prevents indoor humidity from reaching the window and condensing on the cold glass and window frame.

3 & 4) Wooden battens which maintain the fabric stretched out and thereby ensure that the curtain fits tightly against both sides of the window opening. The battens also create air pockets which further reduce heat losses hrough the curtain.

5) A back panel which acts as the final layer of insulation and helps seal the perimeter of the window opening when the curtain is closed.

The reasons why a Kume curtain is so effective in reducing heat losses through windows are:

  1. Still air is one of the best insulators found in nature, and the Kume curtain contains a lot of it. First, between the fibers of the thick polar fleece that is used to make the curtain, and second inside the thin spaces that are created etween the front and back panels by the battens.
  2. When closed, the Kume curtain fits tightly against the top, bottom and sides of the window opening. By doing so it traps a layer of insulating air between the glass and the curtain, and prevents the cold air that forms against the lass from seeping into the room.
  3. A Kume curtain basically works just like a good down jacket on a cold winter day. The air that is trapped in the thick layer of down creates an effective insulating layer, and the tight fit of the jacket around your waist, neck and wrists keeps your body heat in, rather than letting it leak out into the cold environment.

Step 2: Where and How Can You Use a Kume Curtain?

Picture of Where and How Can You Use a Kume Curtain?

1) A Kume curtain can be used on any window whose frame is recessed by at least 1.5" with respect to interior surface of a wall. This is because the curtain works best if it is able to tightly seal the complete perimeter (that is, the top, bottom and sides) of the window opening.

2) A Kume curtain is much less effective when installed on a window that is mounted flush with the interior wall, because the cold air that builds up on the inside surface of the window is able to flow around the sides and bottom of the curtain and seep into the room.

3) When raised, the curtain forms a tight roll whose diameter varies depending on the length of the curtain and the thickness of the material used. For example, a curtain that is 5 ft long and made of two layers of fleece will produce a roll with a diameter of approximately 5". The rolled up curtain does not affect the operation of windows that open outward, sash windows or sliding windows, but it will prevent the operation of windows that open inward. If fitted with Kume curtains, these types of windows will have to remain closed until the curtains are taken down in spring.

Step 3: Where and How Can You Use a Kume Curtain? (continued)

Picture of Where and How Can You Use a Kume Curtain? (continued)

4) Depending on the type of fabric used, Kume curtains can be translucent to opaque. Therefore, they are mainly designed to shield windows at night, when indoor privacy is desirable, outdoor temperatures are lowest, and heat losses are greatest. In certain cases, however, the curtains can also be used during the day: for example, in unoccupied rooms in which daylighting is unnecessary, and in which the windows do not provide any useful solar heat gains.

5) They can be used as the primary curtain on a window, or used in conjunction with a decorative curtain, as shown in the pictures above.

Step 4: Standard Components and Materials

Picture of Standard Components and Materials

For a window opening of width "W" and height "H“, you will need the following components:

1) Front panel

  • Width = W + 0.75", height = H + 0.75"
  • Material = Polar fleece or another thick and flexible fabric that can fit snugly against the sides of the window opening and prevent the passage of air.
  • If the Kume curtain is used as a primary curtain, the front panel can be made with a fabric that best suits the decor of the room (a cotton print for example).
  • You should ideally wash the fabric before making the panels and, as with all drapery, you should consider using flame-retardant fabrics.

2) Moisture barrier

  • Width = W - 0.75", height = H
  • Material = Transparent polyethylene with a thickness of approx. 4 mils (0.004"). You can also use a black polyethylene sheet, but keep in mind that this will make your curtain totally opaque (blackout) even if you use light colored fabric for the front and back panels.

3) Upper batten

  • Section = Approximately 0.5" x 1"
  • Length = W - 0.75"
  • Material = Pine or ideally hardwood.

4) Lower battens

  • Section = Approximately 0.5" x 0.75"
  • Length = W - 0.75"
  • Material = Pine or ideally hardwood.
  • Number = The spacing between the battens should not exceed 20", therefore the number of lower battens needed depends on the height of the curtain.

5) Back panel

  • Width = W + 0.75", height = H + 0.75"
  • Material = Ideally polar fleece or another thick and flexible fabric.

6) Fasteners (not shown)

  • For the back panel we recommend using staples, while for the front panel, which is visible from the room, we recommend using thumb tacks or upholstery tacks. If you are concerned with having these fasteners rust and stain the fabric, you should use stainless steel staples and rust resistant tacks.


A) The front and back panels are a bit bigger than the window opening. This is because these pannels need to completely plug the window opening when the curtain is closed.

B) The choice of materials was mainly guided by our desire to make these curtains very affordable and simple to make. This is why we chose polar fleece for the curtain panels (fleece is inexpensive, insulating, widely available, and requires no stiching to be transformed into curtains), and polyethylene film for the vapor barrier. However, many other types of materials can be used to assemble a Kume curtain. For example, the curtain shown in the last step of these instructables was made using a back panel made of dark blue fleece, a vapor barrier made of transparent polyethylene, and a front panel made of dark blue fleece on which we sewed a flowered cotton print. As you can imagine, this curtain was totally opaque and worked great as a blackout curtain in addition to keeping out the cold.
If you would like to use other types of materials, or even a different structure for the curtain (for example, using a quilted or interlining fabric to fill the gap between the front and back panels), please keep in mind the following points:

  • The fabric chosen for the front and back panels should ideally be moderately thick, tightly woven to restrict the passage of air, and flexible so that it can accommodate itself tightly against the sides and bottom of the window opening.
  • If you decide to use a very thick material for the front or back pannels or for the moisture barrier, please consider what this will do to the size of the roll that you will end up with when you raise the curtain.
  • The curtain should have a moisture barrier placed behind the front panel. Without a vapor barrier you will get a lot of condensation against the cold glass, with a good vapor barrier you will get none (or almost none).
  • The moisture barrier should be made of a thin, flexible and non-breathable material or fabric. It can be of any color, but if it is opaque it will transform your curtain in a blackout curtain even if you use light colored fabrics for the front and back panels.
  • The curtain should fit in the window opening and seal the full perimeter of this opening to prevent the cold air that forms against the glass from seeping into the room.

Step 5: In This Example We'll Assemble a Curtain for a Window Opening That Is 24" Wide and 48" Tall

Picture of In This Example We'll Assemble a Curtain for a Window Opening That Is 24" Wide and 48" Tall

The materials needed for this curtain are:

  • A 24.75" x 48.75" front panel (in this example it is made of thick white cotton canvas)
  • A 23.25" x 48" sheet of transparent polyethylene with a thickness of 4 mils (0.004")
  • An upper batten made of pine with a cross section of 0.5" x 1" cm and a length of 23.25"
  • Three lower battens made of pine with a cross section of 0.5" x 0.75" and a length of 23.25"
  • A 24.75" x 48.75" back panel (in this example it is made of yellow polar fleece)
  • Thumb tacks to fasten the front panel and plastic sheet to the battens. We use thumb tacks for aesthetic reasons since the front panel is visible from the room.
  • A stapler to fasten the back panel to the battens

Step 6: Trace the Position of the Battens on the Plastic Sheet.

Picture of Trace the Position of the Battens on the Plastic Sheet.

Make sure that:

  • The top edge of the upper batten is aligned with the top edge of the plastic sheet;
  • The bottom edge of the lower batten is aligned with the bottom edge of the plastic sheet; and
  • The remaining battens are evenly distributed over the height of the plastic sheet.

Step 7: Slip the Battens Under the Plastic Sheet and Use the Marks Traced on the Plastic Sheet to Align Them Properly.

Picture of Slip the Battens Under the Plastic Sheet and Use the Marks Traced on the Plastic Sheet to Align Them Properly.

Since the length of the battens is equal to the width of the plastic sheet, the ends of the battens should also align with the sides of the plastic sheet.

Step 8: Lay the Front Panel Over the Plastic Sheet.

Picture of Lay the Front Panel Over the Plastic Sheet.

The front panel is slightly longer and wider than the plastic sheet, so when in place:

A) The top of the front panel should be aligned with the top batten;

B) The bottom of the front panel should extend by ~0.75" below the lower batten and base of the plastic sheet; and

C) Each side of the front panel should extend by ~0.75" past the ends of the battens and sides of the plastic sheet.

Step 9: Use Tacks to Fasten the Front Panel and the Plastic Sheet to the Battens.

Picture of Use Tacks to Fasten the Front Panel and the Plastic Sheet to the Battens.
  • Place a tack within 0.5" of the ends of each batten.
    Use enough thumb tacks between both ends of the battens to properly fix the fabric and plastic to the battens.
  • On the upper batten, the spacing between the thumb tacks should be between 4" to 8".
  • On the lower battens, the spacing between the thumb tacks can be increased to double the spacing used on the upper batten.

Step 10: Flip the Curtain Over.

Picture of Flip the Curtain Over.

Step 11: Place the Back Panel Over the Partially Assembled Curtain So That It Rests Directly on the Battens.

Picture of Place the Back Panel Over the Partially Assembled Curtain So That It Rests Directly on the Battens.

The back panel has the same dimension as the front panel, so when in place:

  • A) The top of the back panel should be aligned with the top batten;
  • B) The bottom of the back panel should extend by ~0.75" below the last batten and base of the plastic sheet;
  • C) Each side of the back panel should extend by ~0.75" beyond the ends of the battens and sides of the plastic sheet.

Step 12: Use Staples to Fasten the Back Panel to the Battens.

Picture of Use Staples to Fasten the Back Panel to the Battens.

Place a staple within 3/8" of the ends of each batten. This will ensure that the material maintains its full width and touches the sides of the window opening.

Use enough staples between both ends of the battens to properly fix the fabric to the battens.

You are done!

Step 13: For Additional Information ...

Picture of For Additional Information ...

Refer to the web page for instructions on how to mount the curtain and create the tie to hold the curtain in the rolled position. Other options for assembling the curtain are also described on this page.

This web page provides the curtain assembly instructions in French, Spanish and Italian, as well as in metric (mm) and US customary (inches) units.

Step 14:

Picture of

We hope you like them.

The Kume team


VendicarD (author)2015-12-03

The mean free path of an air molecule at STP is around 2.5 cm.

Gaps smaller than that permit air molecules to jump through the gap and transfer energy from one side to the other. The smaller the gap the greater the heat exchange.

Dead air spaces should be designed to be 2.5 cm or larger. Larger gaps of around 7 cm or larger will permit convection in the gap which will also reduce the insulating factor.

Covering a window with any kind of plastic - paper - tinfoil - whatever that creates a dead air space of 2.5 cm to 6 or 7 cm will produce a dramatic insulating effect and typically reduce heat loss through the window by 40 percent or so.

Translucent or transparent material should be sued so that sunlight can enter during the daylight hours.

Plastic drop cloth works well and is typically translucent. A $9.00 roll will do an entire house for a couple of years if you throw it out each spring.

But why do that?

These curtains are not a bad idea at all. They will do the job, but they are not required for window insulation.

padigm (author)VendicarD2015-12-05

VendicarD - Here are my comments to your post.

1) The mean free path of air molecules at STP is approximately 0.00001 cm.

2) The optimal thickness of an air gap for insulation is approximately 12 mm (about 0.5 inch). This is the reason why this is the distance between glass panes that is normally used in the millions of double-pane windows that are manufactured each year around the world.

3) You are perfectly right when you say that covering a window with a plastic film greatly reduces heat losses, however the logic behind using insulating curtains is as follows: Since most windows are covered with curtains, why not use these elements to further reduce heat losses through the windows? Regardless the kind of windows you have (single-pane, single-pane with plastic film, double-pane, double-pane with plastic film, etc.), covering them with effective insulating curtains will keep your house warmer and your heating costs down.

tanderson28 (author)padigm2016-08-03

I note that one question still remains. Do the Kuma curtains perform much better than plastic film?

If still available to you, the Flir (or other Thermal Camera) can clearly demonstrate the value of the insulation. The plastic sheeting is much cheaper than the insulation. If there not a huge difference in R-value between plastic sheeting alone and the Kuma curtains, I think many people would prefer a very low-cost solution if it was almost as good.

Would really love to see the thermal imaging for comparison!

Sue-LynnK (author)2016-07-17

Great invention! It cut down my energy costs by a lot!!

Lorddrake (author)2016-04-25

Awesome write up . Time to add a new project to the list :)

mongoose5271 (author)2016-01-13

I have mostly older windows in my home and made a couple of these curtains. Made a noticeable difference in the rooms that I installed these, but to my horror, when I rolled them up, there was a ton of condensation on the windows and even ice near the bottoms. I used polar fleece and 2 mil plastic drop cloth (doubled over on each window) and followed the instructions; the curtains fit snuggly into the openings. Any ideas?

padigm (author)mongoose52712016-01-18

Thank you for your comment. I am glad to see that the curtains have made a noticeable difference in keeping the rooms warmer, but I am surprised to hear that you have problems of heavy condensation on the glass when the curtains are closed.

My experience with the curtains installed in my house and in the houses of friends and relatives is that when the curtains are closed there should be no (or a minimum amount) of condensation on the windows as long as the following conditions are met:

1) The vapor barrier panel and the fleece/cloth panels are cut to the correct size. There should be only a small gap (approx. 3/8”) between the sides of the plastic sheet and the sides of the window opening, and when the curtain is closed this gap should be totally filled by the excess width of the fleece panels which is pressed and folded against the sides of the window opening.

2) There is no large hole or tear in the vapor barrier. Even a very thin sheet of plastic (e.g., saran wrap) is enough to stop the movement of vapor through the curtain. The reason why I recommend using a 4 mil plastic sheet is that, according to my experience, it is more resistant and can handle the frequent rolling/unrolling of the curtain without tearing.

3) The curtain really “plugs” the window opening when closed. The curtains needs to seal extremely well the complete perimeter of the window opening. You can check this by closing the curtain during the day and turning the lights off in the room. You should see no daylight seeping through the perimeter of the curtain (a very thin sliver of light here and there is ok, but no more than that). If that is not the case, then you will have a trickle of moist flowing through the gap and bringing condensation to the glass panes.

I am not sure what the problem might be in your case. Could you please post pictures of your curtains (including details showing how the curtain fits against the top, bottom and sides of the window frame), of the windows on which they are installed, and of the condensation? Could you also provide more information on your particular installation?

1) Where are you located?

2) What are the typical nighttime temperatures during the winter?

3) Are these curtains installed in a room with a very high level of humidity (e.g., kitchen, laundry room)?

4) When you close the curtain, after how much time do you start seeing condensation on the glass?

5) Are your windows very drafty? If so, could it be that the moist air is coming in from outside?

Looking forward to your input.

PS: If you have condensation on your windows it is not surprisingat all that it will freeze during a cold night. You have to keep in mind that the closed curtains prevent the heat of the room from reaching the window. Therefore, on a cold night, the temperature of the inner pane of the window can drop to below freezing and any condensation on it will turn to ice.

mongoose5271 made it! (author)padigm2016-01-20

Yes, I had cut everything according to the instructions and there were no holes in the vapor barrier. I made sure to plug the openings and ensure that there were no gaps. Before trying this, I had used the plastic film kits that you can buy at any hardware store. Although, due to the fact that most of my windows are aluminum framed sliders (with no vertical surface at the bottom to apply the tape), I had built wooden frames to fit within the opening, then covered those frames with the plastic and used rope caulk or foam weatherstripping to plug any gaps. Not the most aesthetically pleasing look, but it helped, although there was a little bit of condensation on the metal frame near the bottom but nothing near what I've been experiencing. I've attached a pic (MasterBed.jpg) to show the frames that I've been using. I live in Michigan and up until about a week ago, we've had a very mild winter. In the last week, though, it's been more normal: highs in the 20s and a few times the lows in the low teens and even single digits. Now of the three windows that I've been testing these curtains in, one is the laundry room and another is a bathroom which is right off the laundry room. But the third room is my daughter's, all the way on the other side of the house, which is a ranch by the way. The aluminum framed windows in the bathroom and laundry room are not the most efficient but the window in my daughter's room is fairly new. My furnace humidifier is set to 25%, so it's not overly humid in the house. Since I started having the problem, I've experimented with these curtains to try to figure out a solution. So last night, I tried something different for each of the three rooms. For my daughter's room, all I did was hang the fleece from the curtains from the brackets for the vertical blinds. I knew this would create condensation but I wanted to see the result, and while there was some, it wasn't anything like what I had been experiencing. For the laundry room I extended the vapor barrier (duct taped extra strips on the existing panel that I had originally cut...I know, very hack-like!) on the sides and bottom and then "pressed" it all into the opening. The result was some condensation and a little bit of frost near the bottom portion of the frame, but nothing near what I had before. For the bathroom, I removed the back panel of fleece and then also extended the vapor barrier and pressed the curtain into the opening. This produced only a small amount of condensation, definitely something I could live with. I'm uploading a number of pics that I took this morning (around 6 AM, 15 degrees at the time) for you to see. It seems to me that not having the vapor barrier cut to at least the same size as the opening for the window is the problem, at least for my house; no matter how I folded the fleece to plug the opening, obviously a lot of warm air was getting through to condense on the windows. So I think I'm going to try the solution that I used for the bathroom on the other two windows and see what happens. If it's a good result, then I'll use it for the other windows. The bathroom and laundry room windows have venetian style blinds on them, so I put velcro strips on the upper batten and had to attach that to the opening between the blinds and the window. A tight fit right at that point but nothing I can do about that. I did make sure the curtains were not tight against the windows the rest of the way down to the sill.

padigm (author)mongoose52712016-01-31

I am so impressed by your drive to find a way to make these curtains work optimally in your home.

My experience with the curtains that I installed in my house is that, as long as they are tucked in properly into the window opening, the amount of condensation is minimal. However, as I have mentioned before, I live in an area where nighttime temperatures seldom drop below 20F, and this certainly contributes to reducing the buildup of condensation behind
the curtain.

Over the past few days I have researched various sites that talk about thermal curtains and even contacted a few manufacturers of commercial insulating shades. They nearly all agree that, in very cold climates, condensation on the cold glass is nearly inevitable, and that it is the price you need to pay to keep your rooms warmer and your heating bills down. Many mention that they keep a squeegee or a towel handy to clear the condensation when they open the curtains in the morning.

There is no question though that the tighter the fit of the vapor barrier in the window opening, the lower the infiltration of moist air behind the curtain and, as a consequence, the lower the condensation on the window pane. Therefore, my recommendation would be that you adopt in other parts of your house what you did in the laundry -- that is, make the vapor barrier wider so that it completely fills the window opening … and find a way to deal in the morning with the reasonable amount of condensation that forms overnight.

The solution you applied in the bathroom (i.e., removing the back panel of fleece) is not optimal because it reduces notable the insulating performance of the curtain. In fact, the reason why you had less condensation after making this modification is that without the back panel the curtain let more heat reach the window and flow outdoors, and by keeping the glass warmer this heat hindered the formation of condensation.

Good luck with your curtains … and please do let us know if you come up with the optimal solution.

GEJG1 (author)2016-01-22

I had been thinking of something similar to this design for rooms/doorways that are seldom used
in our house. Planned layers are: window -> 2" gap -> mylar with silver facing window -> double-layered corrugate cardboard -> double-layered corrugate cardboard -> mylar with silver facing room. The idea is I would keep this up year round. In summer, the mylar would reflect sunlight back out of the house.

Some questions:

1) I looked at the R value of cardboard, and it seems higher than polar fleece, so hopefully this will be effective. Your thoughts? (I have done a few international moves so just happen to have double layered cardboard out the wazoo)

2) Learned from your Instructable that I would need fabric around the edges to create a tight seal. Anything other words of guidance/caution?

3) Brandon mentioned a cracked pane if not taken down during the day in winter, so I guess there goes my idea of keeping it up all the time, at least during the cold.

4) Does the plastic sheet HAVE to go behind the first layer of polar fleece? Or would it be just as effective as long as I keep a gap between the mylar and the window? (My sills are 5" deep. I was thinking of affixing this ~2" away from the window from the top of the sill)

3) Also, is there any additional benefit in putting another mylar layer on the back, silver part facing the room, to reflect the heat of the room back and conserve even more energy? Or should I not bother?

Thanks for the fantastic instructable, I am so excited to start on my project!!!!

padigm (author)GEJG12016-01-27

Hello GEGJ1

1) I am sure that a thick piece of corrugated cardboard
should be a better thermal insulator than a layer of polar fleece. However, I
would be a bit concerned about humidity, especially if you are planning to
leave this panel up for long periods of time. Unless your assembly is extremely
tight and prevents the passage of even a minimum amount of humidity, you will
end up with some condensation on the glass. In the case of the curtain, this is
not much of a problem because the condensation either evaporates or is wiped
off when the curtain is rolled up in the morning. However, in your case, it
will probably accumulate over time and soak into your cardboard.

I may be wrong, so please give it a try.

If you do end up with a problem with condensation, I would
try a water resistant insulation material such as an extruded polystyrene
board. They are not very expensive, have a very high R-value, and are not
affected by humidity.

2) In my case, I use the extra width of the curtain fabric to
press against the sides of the window opening and prevent the passage of air.
This is a good solution for a curtain that needs to be rolled up every morning
and rolled down every night, but if you have a more permanent installation you
could use other materials to seal the perimeter of your insulating board (e.g.,
rubber foam strip).

3) Please see my answer to Brandon’s post.

Also, if aesthetics are not a problem (and they should not
really be if you were planning to put a shiny mylar facing the window), you
could consider spray painting the glass white. The paint has to be on the
outside pane of your window and block nearly all of the solar radiation. If
this is not an option and you are very worried about cracking your windows
(which I assume are double pane), you should try to find another option to
shade your windows/doors from the outside.

4) The function of the plastic in my curtains is to act as a
vapor barrier. A vapor barrier should be placed closer to the “warm” side of
the insulated assembly (i.e., closer to the side which faces your indoor
space). Since you are planning to have a layer of mylar facing indoor, this
would act as the vapor barrier on the warm side of the assembly (i.e., you don’t
need to add an additional plastic sheet).

Please note that for insulation purpose, it is generally
recommended to have an air gap that is between 0.5 to slightly less than 1 inch
(your 2” gaps are too big).

5) Sure, a radiant barrier facing the inside of the room
would be useful from a thermal standpoint. On top of that, it will act as a vapor
barrier and prevent moisture from penetrating into your cardboard and
condensing once it reaches the cold side of your assembly.

Good luck!

GEJG1 (author)padigm2016-01-27

Oh my gosh, Padigm, *thank you* for your thoughtful, in-depth replies to all my questions. Helps me immensely. I will report back with my findings once I am done (may take me a few weeks, I have a 3 year old and not as much free time as I would like...)

Thanks again for this great Instructable, you've made a whole lot of people's lives better!

BrandonM76 made it! (author)2015-12-24

I made these curtains according to the instructions for 4 large south facing windows this year. They seal out drafts and it feels much warmer to sit right beside the windows in winter.

Mylar-Layer: I added a mylar layer beside the fleece layer (on the inside) to eliminate radiant heat loss. I measured that the radiant temperature of these curtains equals room temperature, completely removing the 'chilling' effect of standing next to a cold window.

Warning for double-pane windows: During sunny days with cold outdoor temperatures you MUST roll the curtains up as soon as the sun hits them. My double-pane window cracked because it was -4 celsius on the outside-pane of the glass, and 45 celsius between the curtain's fleece layer and the inside-pane of the glass. Repairing this glass will cost more than my energy savings.

padigm (author)BrandonM762016-01-27

Hello BrandonM76

I am very sorry to hear about your window.

When I first posted this instructable, there were several discussions about the possibility of having thermal stresses crack the window glass. I researched this issue thoroughly and below are the conclusions that I came to.

Literature indicates that cracks in double and triple pane windows can caused by various factors, such as poor window constructionand design, and thermal stresses generated by the use of heavily tinted glass (which gets very hot), the use of very dark window frames (which heat up and expand much more than the glass panes), having a window that is partially exposed to direct sunlight and partially in the shade, and the use insulating window coverings which increase the temperature difference across the window unit (for example, if the curtains are closed on a window that is exposed to direct sunlight on a cold winter day). However, given the large number of established companies that have been selling and installing insulating curtains and window coverings for years in harsh climates (and at a fairly steep price - typically 10 to 15 US$ per square foot), I imagine that these types of failures must be the exception rather than the norm. If these problems were very common, these companies, some of which are listed below, would have shut down a long time ago. - EcoSmart Shades (claim to have be R-5.0, or 2 times greater resistance to heat flow than a standard double-pane window) - Window Quilt (also claim to be R-5.0)
- Hunter Douglas

Furthermore, since I don’t believe that my inexpensive DIY insulating curtains outperform these pricy commercial models, I don’t see any reason why a window equipped with a Kume curtain would be more prone to cracking than a window equipped with an EcoSmart Shade, a Window Quilt or a Hunter Douglas Honeycomb shade.

Regardless, it is better to be safe than sorry and as a result I will put a note in the instructable warning users to avoid leaving the curtains closed on windows that may be exposed to direct sunlight on a cold winter day.

PS: Could you please let me know which is the window pane that cracked (inner or outer) and where on the glass did the crack appear? Thanks.

BrandonM76 (author)BrandonM762015-12-24

You may notice in the picture that I failed to get the fleece to fit above the top pine battens. That gap at the top does not leak any cool air (because cool air sinks) however the gap is causing condensation on the inside of the glass.

You guys should aim to do better than I did on this project.

signeinla (author)2014-09-04

I am wondering if, in fact, something like this could be used to reduce the heat coming into the house from sunny exposures, as someone commented below. I think you would have to use different materials, something reflective. Would you have any ideas? I love what you have done here and would love to tweak it a bit for our hot California summers.

skiwolf9 (author)signeinla2015-12-03

I have two southern exposure windows in two bedrooms. I bought some 70% shade screen on the internet, 3/4 PVC and some pvc clips that'll hold the shade cloth to the pvc pipes. Hung them from the rafters about a foot from the windows. No more hot rooms in the summer. Did the same thing over the driveway, cool cars instead of sun blasting them all day, making them hot as well as uv damage to paint.

padigm (author)skiwolf92016-01-26

You are spot on. The best way to reduce the solar heat gain through a window is by shading it from the outside.

padigm (author)signeinla2014-09-04

During the summer, these curtains can definitely help reduce the heat load coming from windows that are exposed to direct sunlight. Having a reflective panel (e.g., aluminized fabric) facing the window would be best, but this might create some aesthetic problems since you would be able to see the reflective material from the room when the curtain is rolled up.

An intermediate solution would be to make the exterior panel from a light colored fabric (e.g., white or off-white). As a matter of fact, if you used light colored fabrics for both panels, you would end up with a translucent curtains that would allow light into the room when closed. In this way, you would be able to keep much of the heat from direct sunlight out of the room while still allowing the room to be illuminated with natural sunlight.

The first curtains I installed in my house had a dark blue panel facing the window, but even so they were pretty good at blocking the heat from direct sunlight when closed (I live in Chile where summers are just like in California). However, this dark blue backing also blocked off all of the light and basically had the same effect as a blackout curtain -- the room was pitch dark.

Ernst59 (author)2015-12-22

Dang it! Had to make one and goof it up to find this. There is a discrepancy between your listed msrmnts. and your assembly instructions--- In step #4, you state this:

1) Front panel (and/or back panel)

  • Width = W + 0.75", height = H + 0.75"

3) Upper batten Length = W - 0.75"

4) Lower battens Length = W - 0.75

Then, in step #8, comes the problem----

C) Each side of the front panel should extend by ~3/8" past the ends of the battens and sides of the plastic sheet.

That should read "should extend by 3/4" past the ends of the battens", should it not? The panels are 3/4" wider than the actual window opening, for an overlap/tuck of 3/8" on either side, and the battens are 3/4" less than the window opening, for an allowance of 3/8" on either side. In other words, the width of the panels is 1-1/2" wider than the length of the battens, so that, when the battens/plastic are centered on the panels, there should be a 3/4'' overhang on either side, as opposed to 3/8''.

Clear as mud? The devil in the details and all......

Fortunately, the "goofed" panel is going in a corner window where only one side of it will be visible. Shouldn't affect it's operation. Onward with the other 5!

Great shades, looking forward to the finished project!

padigm (author)Ernst592015-12-22

You are right! Thank you for pointing out that mistake in the assembly instructions. We had checked and rechecked them, but never saw that mistake. We have corrected it in the instructable, so hopefully those coming after you will make perfect curtains.

Thank you once again, and please post a picture of the curtains you made.


yellowcatt (author)2015-12-03

Using Mylar film (space blanket) for the moisture barrier should reflect more heat back into the room.

padigm (author)yellowcatt2015-12-13

You are perfectly right, using a space blanket as vapor barrier should improve the design by reducing heat losses by radiation. The thickness of the blanket or vapor barrier doesn't matter, as long as the material is tough enough to resist handling (daily rolling and unrolling) without breaking.

By the way, the instructions for these curtains are available in metric and US measurements in English, Spanish, Italian and French at the following website


waltbosz (author)yellowcatt2015-12-12

I was thinking the same thing, but are the space blankets thick enough? The instructable calls for 4mils thick plastic. The space blankets that I have are very thin ... well like a Mylar balloon.

yellowcatt (author)waltbosz2015-12-12

It is a moisture barrier, as long as it stops moisture a slight dıfference in thickness should be unimportant.

I had to look up the meanıng of mils as I was not familiar with the term. It seems to be an Americanism for a thousandth of an inch. what the rest of the world would call a thou. I would rather sick to metric measurements to avoid confusion.

DanieleZ (author)2015-12-03

If you live in a 9m square room with just a window and exit, insulating the window and the door, will you die from room oxigen deprivation?

Michael013 (author)DanieleZ2015-12-04

CO2 toxicity would be your first problem, not oxygen. Does your sealed room contain any calcium oxide (quicklime)?

DanieleZ (author)Michael0132015-12-05

I'm not sure about quicklime, but what it has to do with co2 ?
Sure I might die from co2 intoxications like astronauts in outher space but this takes a long time too don't you think ? And what if I've got a something to convert my co2 to oxigen: Like a nice plant ?

absolutekold (author)DanieleZ2015-12-09

To quote "The Martian" movie we're going to have to science the S@$% out of this. My previous estimates weren't wrong but it's true they didn't really take into account CO2. However before we call NASA to get their space breathy tech let's see what a problem CO2 really is. While the numbers vary widely I'm going to settle for a middle of the road estimate of 200 mL per minute as a persons CO2 "output". Rather than write another small book I'm just going to attach a snapshot of a spreadsheet. Those are the raw volumes for an empty sealed room but like my previous assessments and even dividing the numbers in half for clutter it's 8 days until you get to the headache stage. Bottom line if you feel crappy and you think it's because CO2, Grow some herbs, have some potted plants, maybe do an aquaponic setup and open the window / use a fan when the weather doesn't suck. I just hammered that out in 10 min so there are spelling errors and the science is pretty loose and fast but it's still in the right ballpark. If you keep to my air exchange rates in my previous comment that accounts for 100% of breath volume so it's overkill.

Nyxius (author)DanieleZ2015-12-07

Air can be bubbled through a solution of quicklime to absorb the CO2 from the air. CO2 toxicity is a much bigger problem than O2 depletion. We only consume a small portion of that 500ml worth of O2 with each breath, but we can only tolerate a 3% change in CO2 levels before it starts to affect your metabolism and thought processes. The quicklime mechanism is the old stuff used by astronauts. The new systems rely on the different thermomechanical properties of CO2 to seperate it from the air mechanically.

absolutekold (author)DanieleZ2015-12-04

Well lets do a little math. I've got to make some assumptions but lets assume you are living in a 9m by 9m by 2m room. That's 162 Cubic meters or 162,000 L of air minus the volume of stuff in the room. An average person breathes in 500mL of air every breath so you've got about 324,000 breaths to consume that much air. With a relaxed breathing rate of about 20 breaths per minute you'd be in real trouble in just over 11 days if you are alone, in a sealed space of that size and not prone to becoming excited. Basically you'd die of dehydration first. Real living spaces have a significant amount of clutter so lets figure half of the air volume gets eaten by junk, also I'm going to negate the fact that you don't consume all of the oxygen each breath to err on the side of safety, you'd still need to be sealed up for about 5 days. To keep with plenty of air you need to exchange 0.01m^3 (or 0.35ft^3) per minute. Now I don't have good numbers for the air exchange for you opening and closing your door but if you spend a fair amount of your time out of the room every day I'm not seeing adding some insulating drapes being what does you in if you haven't suffocated from living there already. I can tell you that you're below code for effective ventilation to keep the air quality to a high standard but unless you're in the worst designed concrete bunker (who puts a window in one anyway) the building itself breathes enough to keep you alive with you occasionally entering and leaving.

DanieleZ (author)absolutekold2015-12-04

+1 @absolutekold

KzooK1 (author)absolutekold2015-12-04

Awesome post, awesome answer. Thanks for both.

VendicarD (author)DanieleZ2015-12-03

Do you have duct work?

DanieleZ (author)VendicarD2015-12-04

No mostly here appartements are not equiped with duct work

Engineering (author)2015-12-08

A lot simpler solution is Silver Bubble insulation found at most big box hardware stores. As with the curtains these a little in R value (about 1-4 depending on the brand and construction), but the biggest savings come reflective nature of the sliver Mylar for heat in and cold out, the additional bubbles between do exactly what the curtains do and they are air tight. Which is why those emergency silver Mylar blankets work with no insulation.

padigm (author)Engineering2015-12-08

You are perfectly right, there are lots of simpler solutions if you are not concerned with aesthetics or the convenience with which you are able to open or close the insulating layer over the windows. In such a case, instead of limiting yourself with an R-4 silver bubble insulation, you would be better off covering the window opening with a piece of 2-inch thick extruded polystyrene (R-20) that is covered with a radiant barrier.

Please keep in mind that radiant barriers reduce heat losses or gains by radiation only. Therefore, a radiant barrier always works better when used in conjunction with a layer of insulation which is able to reduce heat losses or gains by conduction.

jeanniel1 (author)2015-12-07

This is great! My bedroom is FREEZING at night, and I have not only two windows, two large patio sized door / windows, but four skylights, and no wall or ceiling insulation (yes, WHAT was the owner thinking - or the contractor for that matter?!). I'm going to do this for at least the two windows by the bed, and work to the patio sized window / door. Great idea.

padigm (author)jeanniel12015-12-08

Great! Tell me how it goes and share the idea with your contacts and friends

VendicarD (author)2015-12-05

1. You are right. My source - a window manufacturer - was wrong.


10 **-7 it is.

Anthony. (author)2015-12-03

It seems like a good idea, particularly in rural areas, but it looks like it cannot be rolled up to see outside on a mild day, or am i wrong? Can it be used like any shade that rolls up and down?

KzooK1 (author)Anthony.2015-12-04

You can make a sling to roll it up & down.

padigm (author)Anthony.2015-12-03

It basically works like a roller blind: the only difference is that you need to roll it up by hand.

There is nothing really rural about these blinds. You can make them as pretty or ugly, as rural or urban as you want.

Brian H (author)2015-12-03

Here's another "trick" -- Set a small fan on the floor in a corner, directed upwards, pointed at the corner. Leave on 24/7.

This is a quick version of the pro version, a hollow corner column containing a fan. The effect of either is to mix hot ceiling air with cold floor air, making an even, comfortable temp throughout. Saves up to 40% heating OR cooling!

kandie.watson.56 (author)Brian H2015-12-04

Brian H
there are 3 of us college students living in a old shotgun house, we only have wall heater with 3" fans in them ( there installed, look like there space heater) we use box fans to circulate but there isn't one in kitchen n appears to be no insulation anywhere, hardwood floors etc ...
Anymore cheap cheap ideas for some broke college students

KzooK1 (author)kandie.watson.562015-12-04

Wall tapestries will help. Look for a local carpet store, you should be able to get remnants cheap. If they're small, sew several together to make a larger rug or tapestry. You can also just hang sheets or blankets on the walls; even something thin will help some.

padigm (author)Brian H2015-12-03

Please not that whatever trick you use to mix the hot air that naturally rises to ceiling with the rest of the air in the room, you will still save energy by losing less heat through your windows (and walls, and roof and floor, may I add).

NIESAMON (author)Brian H2015-12-03

Save gas :D Loose electric :( Im still going to try it tho Ha HA

jpayton (author)NIESAMON2015-12-03

Actually using a fan to mix air by pretty much any method provides better heat usage then the electricity that it uses. I personally use ceiling fans as they get the warm air moving into the cold. The difference is probley non-existant but it feels warmer to me. But I have poorly insulated floors so that might be some of it.

suancol (author)2015-12-04

Since I suffer with SAD I am always aware of needing natural light. I put a polar fleece curtain liner behind my curtains. No hemming except attaching it to liner tape from sewing store. Cuts heat gain and heat loss amazingly and very simple and easily done. Can be moved to new home too. For summer heat, as many people said, block it before it enters the house with blinds or vines. For winter heat retention add a pelmet above the curtain or a rolled up towel as warm air sneaks behind the curtain and is cooled down quickly. Carpet on the floors helps too.

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Bio: I am a mechanical and environmental engineer, and I help companies pollute less by making a more efficient use of energy, water, materials and chemicals ... More »
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