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How to insulate a cooler box Answered

I have just bought a plastic cooler box. It is two boxes in one: an inside lining, an air cavity, the outside case and  of course a lid and handle.. I would like to improve the insulation. I have a 750ml can of expanding polyurethane foam which I thought of spraying into the cavity. It will dry in an hour. I can work out the exact volume  to be filled with  the foam by prefilling it with water and measuring the amount of water that pours out of the cavity , but I do not know the best way to apply the foam. Any ideas, please. For example should I wrap the inner box in anything before pushing it into the wet foam that I  spray against the inside of the outer case?



This website http://www.engineeringtoolbox.com/thermal-conductivity-d_429.html gives a very low value for the thermal conductivity of air, 0.05, very close to that of plastic foam, could use air as the primary insulator against loss due to conduction. Paper would be used as a medium to prevent loss due to convection of air. This looks like a pretty efficient and low cost way of insulation but am not able to find any such use on the internet. I really can't understand what I'm missing here. Can one not achieve an r value of close to 20 by just filling a 5 inch cavity with air and creating pockets using paper. This could be just stuffing shredded paper or filling the space with paper straws. Is there a problem here with no air tight spaces. Or is my basic premise incorrect.

Depending on the type of spray foam you have, that stuff expands a whole lot and creates enough force to bend or warp plastic if it is trapped in a cavity. It sounds like you can pull out the inner liner of your cooler. I would just spray a few blobs of the foam on the bottom and put the liner on top of it. You may want to then have something rigged up so it will float up to the proper height or held there when the foam expands. You just need some patience to watch the foam ooze up a bit from the bottom to the sides. When that is cured and hard, you can finish and fill up the side walls. I would just use clear packaging tape to mask all over where you will cut away the excess cured foam. You may need to bend the liner top lip to get that application straw or tube in there to shoot the foam. I guess you could wrap your liner in plastic wrap and the wrap will remain embedded in the foam if you want a removeable cooler pan. I don't think there is any good release agent since that foam sticks to anything. Good luck.