For those of you rushing into Halloween, this thing called Wonderflex might be able to do the trick.
While doing some research on insulation foam for my goggles I came across this site: http://www.costuming.org/wonderflex.htm It’s a FAQ about something called Wonderflex.
There are some amazing photos of what people can create with them. If you are in rush, or looking for a low budget option for your pack parts, stunt trap, Iona, etc… this can be of some help! They state that Wonderflex differs in price depending on whom you purchase from. A full sheet ranges from $27.50 to $50.00 US before shipping, but apparently it can be bought at Home Depot.