What are coolers (Igloo, Thermos, etc) actually made of?

Question

I noticed that those new "Extreme 5-day" coolers have really thick walls. So what are the walls made of? Why are they good insulators?

Answer 1

The cases are usually polyethylene, with air in between the inner and outer layers.

The more efficient ones are filled with low-density polypropylene foam in between the inside and outside plastic.  

The super efficient ones, just use a thicker layer of foam.

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