Originally Posted by TimpanogosSlim
Also worth stating that the cooler lids are often just hollow plastic. Some people use expanding urethane foam ("great stuff" - cracks and gaps version) to insulate them.
I keep meaning to try that, but haven't gotten around to it yet.
Yup, I did this too right from the word go. I had no trouble getting the Great Stuff to fill my whole lid. Every little bit of heat retention helps in my book!