My home was built in 1951 and it has this fiberboard, it feels like paper, peels and separates like layers of paper. The home was modular construction. I'm screwed in terms of exposure already, but if somebody knows for sure I'd rather save the money than getting it tested because I've already exposed
This is a piece of it having been ripped in half, with a layer of paint, it's a brownish/tan color on the back but the inside is gray: