Most How-to's say to use tool steel and they are not wrong... However, if you need a hammer you can't find on-line or afford, then you might go traditional and forge one out what's in the scrap pile....
maybe cotton wool or fabric or sponge or maybe even plastic i suppose you can have softened wood.you cant have blue tak or metal or anything like that i hope this helps you make some pairs of ear...
Milar is a common material for "space blankets". It is extremely compact, and can be amazingly warming. Fleece and Wool have good thermal properties, and are relatively effective even when wet.