I think the best stuff to use is Owens Corning #703 ridge fiberglass it's easy to work with, it stands up by it self. I'm from Pittsburgh I got mine at George V. Hamilton Inc. in Mckees Rocks 412-771-0900
www.hamiltongv.com mine was 2" x 24" x 48" sheets. Cover the hole inside with metal before you fire it up lol lol wow did that stink. Rock wool is good also. And you can cut it with a little hand saw
