Make a Well-insulated Travel Cooler





Introduction: Make a Well-insulated Travel Cooler

About: the letter B

This may not be a problem for most people, but I have a habit of keeping drinks and food in my car so that I can use them on my work breaks. This becomes a problem in the summer when the car gets hot (140dF). Nobody likes drinking their DrPepper at 140dF. Simple plastic lunch coolers with thin foam filling and solid lids won't keep cold for long at all. After much debate over the possibility of using active refrigeration schemes, I decided that the easiest and most reliable design was simply an icebox. This would also make the cooler more portable and lend it to a variety of uses.

Step 1: Think First

As for design, we want the box to be absurdly insulative for a couple reasons. First, more insulation results in a longer melt time on a given mass of ice. That's simple enough. As long as there's solid ice, the block's temperature remains relatively constant. Second, the greater the disparity between the thermal resistance of the box walls and that of the air inside, the less of a temperature gradient exists between the ice block and the walls of the cooler. This is what allows me to avoid using shaped or distributed (bulk crushed ice) charges.

I personally needed it to fit behind the passenger seat in my car. This limited the dimensions, so I had to find a size that would work with different arrangements of beverage containers and ice containers. I chose an internal box size of 7W x 10.6L x 10H (inches). Different applications would require similar planning.

I considered a few materials for the insulation: FIP polyurethane foam inside a cardboard box, EPS (beaded polystyrene foam), and extruded polystyrene foam. Since the first two ideas suck and I already had a sheet of 1.5" pinkboard, I decided to use that, thus giving the box its absurd 3" thick walls.

Step 2: Cutting Things, Building Things

I reccommend using 1-1/2" extruded polystyrene. The extruded variety is better suited to this application than the white beaded EPS. EPS will more readily absorb water between the cells and isn't as strong. Other thicknesses of foam are also available to make thinner or even thicker boxes.

All the panel sizes were cut on a radial arm saw, though one could easily do this with a circular saw or a hot-wire cutter. I could've done a bit better on a few of the pieces, but the biggest problem wasn't my measurements. It's that the sheet was bowed and all the edges were not perpendiculars, but radials. Make sure to get a flat sheet, especially if your foamboard is thicker.

The box is assembled using a polyurethane glue such as "Gorilla Glue" or any of the similar glues on the market. The advantage here is that they have a good bond strength and they expand to fill any gaps between the sheet edges. The assembly of my box was made difficult by the bowed panels as they would constantly leave gaps at their edges. That's what clamps are for though. The clamps are pretty necessary anyway, as the polyurethane glue doesn't have a very high initial tack. If your panels are flat, you could probably get by with using tape to hold it tight.

Step 3: Foil Facing

Since the cooler is going to sit in the car being irradiated by the mid-day sun, it would be best to reduce the amount of energy being absorbed by giving the cooler a reflective surface. The quickest and cheapest way about doing this is by using an aluminized mylar sheet- AKA space blanket or emergency blanket. This only costs a couple bucks and is about as effective as placing the cooler in the shade. That may not sound like much, but it's a good deal if you can't put it in the shade.

For the sake of durability, the aluminized face should be positioned toward the inside. You can identify the aluminum face of the film by rubbing on it with your finger (the aluminum comes off) or using an ohmmeter.

The mylar is attached to the box using a spray adhesive. I used green label 3M Spra-Ment, although there are several compatible adhesives available. CHECK THE LABEL. Not all spray adhesives are safe on foamboard. Cover the box by rolling the sheet around the sides, leaving the excess to form flaps to cover the top and bottom. If you can wrap a present, you can do this. It's best though, to spray the box (not the film) one side at a time. The glue tackifies quickly, and you can't reposition the film on tackified glue. Once the film is in place, It might be a good idea to use clear packing tape to hold down all the edges and reinforce the corners.


After everything is assembled, wrapped, taped, etc. and the box has aired out for a while (important), it's ready to use.

To base my expectations, I did a rough calculation involving the wall thickness, radiant area, thermal conductivity of the foam and the fusion enthalpy of water. Given that the temperature in the vehicle swings from 65dF during the night to as high as >140dF during the day, I found an average of 100-105dF to be reasonable for the calculations. The results indicated that the box should be able to keep 2kg of ice for around 27-30+ hours. Increasing the box dimensions independent of wall thickness will reduce this time. Increasing wall thickness and the mass of the ice charge will increase this time.

After running the box in the car for a few weeks, I can say the calculations are pretty accurate. The ice blocks come out of the fridge at 14dF. With 4kg of ice, it can easily maintain acceptable temperatures for four days even when it's opened four-six times per day. I just rotate different sized ice blocks (frozen beverage bottles and 1/2gal milk jugs) to accommodate different container arrangements and expected durations. It might be a good idea to make your box fit available rectangular ice bottles. Round ice blocks waste a lot of room.

The coldest I've ever had the bottom of the box (coldest part) was about 19dF. The warmest I've ever had the top of the box (warmest part) was about 42dF. Such high temperatures are only reached when the box is in the sun, the ice charge is growing small, or the lid has been recently opened. It averages between 34-38dF most of the days.



    • BBQ Showdown Challenge

      BBQ Showdown Challenge
    • Backpack Challenge

      Backpack Challenge
    • Stick It! Contest

      Stick It! Contest

    26 Discussions

    If I put this food container in the middle of those insulation materials and box it up. Throw in few icepack at the bottom of the food container, will it be good enough to store raw chicken for like 6 hours while maintaining temp of <40F to ensure that the meat don't go bad?


    Can you use this method to make a delivery bag? Maybe a large regular bag lined with Mylar ice packs? Would that work? Or is there any other to make a cooler delivery bag?

    1 reply

    For ice pack, for example Cooler Shock, 1 large = 6 lbs of ice. Ice chest companies suggest 2/3 ice or 6 lbs/day. for a long trip and that is with a hard side cooler.

    Foam camping beds would be good for adding insulation to a soft sided bag. The have a little less r value, 3.5 vs 6.5 per inch than his XPS board.

    "Thermarest Ridge Rest Solar Sleeping Pad" would be a good one to use. line cut to size and line inside or outside of cooler with pad. Should help.

    Cooler will be heavier with ice or ice pack, bigger or less interior space for longer chilling time,

    3" is not that thick. In Australia there is a company that makes portable fridges for 4wd etc with 125mm (5 inch) thick walls. It is 24% more efficient than 75mm (3 inches) thick wall fridges. Most people don't have the room in theirs cars, so use cheaper thinner walled ices boxes. Simply adding 25mm (1 inch) to a portable fridge which have very thin walls of about 40mm (1.5 inches) to start with, will reduce battery load by roughly 25%. If you are building a custom ice box chuck as much extruded polystyrene at it as you possibly can. Another option is Aerogel, but it is expensive and I believe more fragile. Aluminized material only works with a radiant heat source, eg the sun, hitting the ice box. So make the outside of the box silver or white. Keeping the ice box/fridge &/or car in the shade will be more beneficial, & not cost anything. I have had 65°C (149F) in the car without really trying in Australia. Your Esky as we call them (ice box) takes a real hammering. 75mm (3 inches) with care in the shade in summer with a solid block of well prepared ice will last 7 days. The solid block of ice should be 50% or the volume of the fridge. The ice box should also be pre-cooled for 24 hours. Also have an official "esky door opener" so the other person can get the items in & out of the fridge at quick as possible & you can provide a third hand! Opening the ice box is a 2 person task, teamwork to reduce opening time & number of times of the ice box door is of the utmost critical importance! Kids are not allowed to open ice boxes if you want/need to keep your ice as long as possible!

    1 reply

    Forgot to add. if you really need to get a few extra days of performance out of your ice box. Freeze a half a dozen 1.5 litre soft drink bottles an simply place them on top of the ice box. Place a sleeping bag over the top them. As they melt first you have drinking water to consume. You will get 10 days out of your 75mm ice box with a bit of care and planning.

    I am currently working on a similar project; my father-in-law's Christmas gift. It will be for holding beer at a cold drinking temp when he is out on the BBQ pit. I am using wood as an outer, protective shell, then using the extruded foam to build the actual cooler inside the wooden box.

    Hi i was just wondering how to make a small version of these just like 6x6x6 or something

    Great design! I've been thinking of building something similar but use it for thermal cooking. How big a pot will fit in your cooler? If you can get a sizable one inside, you may want to try cooking in it. I would try with beans. Would a pot of raw beans brought to a boil and placed in your thermal box be fully cooked by the next morning? I'd love to know that!

    3 replies

    I don't know how one would do cooking in such a thing as fashioned. The polystyrene will become soft and possibly melt partially if a 100dC object is placed on it. Avoiding that is trivial, but I don't understand the practicality of putting partially heated food in a box without a heat source and expecting it to cook.

    If a time-temperature figure is sufficient to determine whether and to what degree an object is or can be cooked, rough figures of the thermal resistances and heat involved in the system can be derived easily. The rest is just integration of an inverse exponential (temperature) over time. If you choose to do so, you would certainly want to use dimensions appropriate for your particular application. Thermal conductivity of XPS is around 0.033-0.034 W/(m*K), and is lowest only when the material is kept dry.

    Putting foil on the outside wouldn't make any sense in your case, though i have a feeling that using mylar on the inside of such a box might be problematic with such high humidity (the aluminization tends to oxidize away if the mylar stays damp). Aluminum foil may work better if a reflector is desired.

    Hey! Thanks for your comment. This kind of cooking is popular in Asia, where they use vacuum insulated pots, but they're expensive. It's practical because food will never burn, and it saves energy. I haven't built such a box but was wondering if you would try it. The polystyrene would probably be fine with 100C, but maybe some cork underneath would help. With such thick walls, a reflective lining may not be needed. Here's an example of this cooking:

    I might have to try this, or some variation of it since I always bring my own beverages when I go somewhere.

    Try ceramic tile mastic for bonding foam. Works great for me.

    You have done an amazing job! I made a cooler similar about 15 years ago, a full blown cooler size and only used one thickness of the 1.5" pink, all cut on a radial arm saw also. I used the rubber spigot from a wine cask fridge box on the side to drain water. Saved money on ice, kept things colder longer.

    When I did mine, I used the cooler box inner. Most can be unclipped from the outer very easily. Then I have a wipe clean interior. I built the foam around the inner, finally putting 6mm ply around that to protect the foam. I kept the original lid and used a single sheet of foam on top. As cold air sinks, it is not so important to have double insulation on top and means I have a well fitting lid to seal onto the cool box inner.

    I have used "Enerfoam" adhesive for joining foam pieces together. It is available from some building supply stores having used it on ICF's (insulated concrete forms) for a concrete foundation wall. It bonds well and expands to fill any voids. It sticks to most things so be careful when using it.


    I really like this. Very useful and original. I think I'm going to have to make this, but I would probably do it upright with a hinged door. and keep it in my room.

    1 reply

    There is an advantage to having the "chest freezer" style orientation rather than the upright fridge one, in that while the door of an upright fridge is open, the (heavier) cold air falls out of a fridge, and is replaced with warm, moist air.

    That warm, moist air is an extra thermal load for the refrigeration unit (in an electric fridge) or stored refrigerative capacity (ice, etc., in this kind of cooler) to remove, and so will lead to your stored stuff heating up faster, or your stored refrigerative material running out sooner.

    Dr. Pepper on work breaks eh??? looks suspiciously like milwalkee's best light haha Great Idea.

    Nice instructable! It could work well in a stationary application as well as a portable application, as a substitute for those inefficient mini-fridges. In a climate-controlled room, you'd have to add ice much less frequently

    Can I suggest adding it to the new group I created, energy efficinecy?