Instructables

Make a well-insulated travel cooler

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.
 
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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.
cgarcía421 year ago
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!
ElFantastic0 (author)  cgarcía4211 months ago
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: http://www.youtube.com/watch?v=qSENxdh-3ec
chrisnotap1 year ago
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.
snafell1 year ago
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.
slim4513 years ago
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.
enerfoam.jpg
Kevvixx6 years ago
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.
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.
jackbomber5 years ago
Dr. Pepper on work breaks eh??? looks suspiciously like milwalkee's best light haha Great Idea.
LowEnergy7 years ago
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?
Two thoughts/observations: 1. Restricting air flow/exchange has helped us keep cooler items frozen longer. We do that by first placing a draw top garbage bag in the cooler and closing the bag in between openings of the cooler. We have kept the ice chest items frozen in a regular picnic cooler for two full days that way. In this super insulated version that might be four days. 2. There are fiberglass/plastic backed panels of pink board used in the cell phone stealth business. If you could get your hands on some of that for the bottom you would have a particularly strong base from which to add handles or carrying straps.
ElFantastic0 (author)  nepperhanman7 years ago
actually, that trashbag idea is pretty slick, as air transfer is a problem with the repeated draft caused by popping open a tight-fitting lid. it would also keep condensate from the foam's surface, reducing absorption. i've kept ice in this box nonstop from the day i posted this instructable, and it seems that it's absorbing a small amount of the condensate water into the foam, reducing the effective "runtime". I plan to let the cooler dry out completely this weekend, then i may try your idea.
ve2vfd7 years ago
I like it! I'd probably make a flat ice pack (freezer ziplock bag maybe?) thats permanently attached to the lid.
ElFantastic0 (author)  ve2vfd7 years ago
I'm contemplating using a bag-lined aluminum box to fit between the rows of cans, but I'd have to make two so that i could rotate them
Myself7 years ago
I've considered doing exactly this for quite a while. How did you waterproof the bottom, or does it just leak meltwater on your seat? I assume the glue forms a pretty good joint, but is that all you rely on? Keeping the ice above the drinks would reduce the thermal stratification. Do you think the pinkboard is strong enough to support an "ice hammock" hanging from the lid?
ElFantastic0 (author)  Myself7 years ago
i used glue to seal all the internal seams, though a polyethylene liner would be a good idea if you intend on using bulk ice, since even pinkboard probably absorbs water eventually. Something like the material that waterbed liners and rubber swimming pools are made from would be a good candidate. and yeah, putting the ice on top is a good idea. the pinkboard is pretty rigid, but you can't really put fasteners or anything on it. i originally thought about gluing an aluminum plate (14 ga) to the underside of the lid to screw an existing ice bottle to. I'd imagine you could use a similar scheme to attach different ice forms. The trick would simply be to distribute the force across the surface.