That's pretty neat I never saw one in the GEM box like that. The 1960's Flexo catalog describes them as a "Skinner Type" air filter. They are pretty tough to come by especially with the West Bend script cover. I bought a whole junk motor one time just to get the air filter off it. As far as what that material is I saw a hillbilly on Youtube one time messing with an old chainsaw and he said the filter looked like it was made out of tree bark! I was laughing but he's probably right.
Like AJF termed it, it's some type of porous fiber material but I'm sure if it's natural or synthetic and I'll be darned if I know where to get something like that these days. I scrubbed one clean with Safety Clean solvent and blew it out with compressed air and it's hard to tell if you even got it clean or made it worse. Always blow the compressed air from the inside of the element out. It''s very dense material whatever it is .