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:

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%.
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.
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?

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:

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.
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.
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?

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)

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

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.

Notes:

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

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.

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.

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.

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.

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.

Step 11: 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.

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 ...

Refer to the web page www.kumeproject.com 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.