We have a cottage in Connecticut that was built in the 1930's or 1940's. The ceilings need to be painted.

BUT. The ceilings are made of panels. Four feet by ten feet. A few years ago, we had to replace one, and we were told that these panels are actually a kind of heavy cardboard, popular at the time.

The guy told us the name of this material, this cardboard -- but now I can't remember what he called it.

Does anyone know?

Thanks --