What type of insulation was common in converted attics?

Good day!

I am currently in the process of renovating a converted attic. On the sloping ceilings, I noticed gray panels whose material I cannot verify. They are gray-colored panels, quite crumbly in texture, which are applied on top of styrofoam panels. In the middle of the texture are stiffening threads made of fiberglass or plastic, and on the top side, there is a type of paper attached. The apartment seems to have been renovated in the 1970s, at least the bathroom with the forest-green toilet looks like that.

I am fairly certain that they are neither brominated panels (almost 100% asbestos) nor Eternit panels (10 to 20% asbestos) – but then what? Could it be a mixture of plastic and asbestos? When you hold fire to it, it smells like plastic; the texture is like hard foam, roughly, only quite crumbly.

I have now found an image on the internet that, in my opinion, looks like how the entire board could look: