You can get discount foam if you buy a tractor-trailer load of it. It seems to go for about half price that way. Foam type, thickness, and quality varies, but is stated ahead of time. If you can get several households together it might pay. Not free, but...
Dan
You don't know me, but I've been looking all over the world for. Thanks to the help from this tiny ad:
Gardening and natural building at a delightful pace