where to get it?
is it cheap?
come it wat sizes?

mid density fiber wood. Usually comes in 3/4" thick and used to make enclosures for subs. Dunno about the price.

Nowadays quite expensive & most of it for export market even-though our local manufacturers are one of the largest in the world. Ones available for local usage are all B-graded but still selling at a high price; that's why nowadays most enclosures are using plywood instead, of course sound not so good-lol.