I think you are referring to Styrofoam. The difference is the aircraft grade is guaranteed to not have any voids or lumps. That is kind of important when you are doing hot-wire cutting.
If you are talking Urethane foam, don't do any hot-wire work. The urethane puts out a toxic gas when it melts similar to the mustard gas used in World War I. Cut it with a knife or saw; sand to your hearts content. Gasoline will dissolve Styrofoam instantly. Urethane is inert with gasoline. Making a fuel tank? Use urethane foam, fiber glass and vinyl ester resin. Vinyl ester is gasoline and alcohol-proof. Do not use epoxy for gasoline contact. Alcohol found in automotive gasoline will slowly dissolve any epoxy. Read the descriptions and cautions in the Aircraft Spruce catalog under Foam. Sid Wood KR-2 N6242 Mechanicsville, MD USA They are the same as far as I know. Model builders have been using the same foam for years. I'm using Owens Corning (pink) foam in my KR1. Fred Johnson Reno, NV -----Original Message----- I have a question for the list, what is the difference in the 2lb. foam you can buy from wicks or Aircraft Spruce and the stuff you can buy from the lumber company ? Thanks for your reply _______________________________________
