ᐅ What type of insulation is commonly used in converted attic spaces?

Good day!

I am currently remodeling a converted attic. On the sloped ceilings, I noticed gray panels made of a material I cannot identify. These gray panels are quite crumbly in texture and are installed over polystyrene insulation boards. In the middle of the texture, there are stiffening fibers made of fiberglass or plastic, and a type of paper is attached to the top surface. The apartment seems to have been renovated in the 1970s, at least the bathroom with the forest-green toilet indicates that.

I am fairly certain that these are neither brominated panels (almost 100% asbestos) nor fiber cement boards (10 to 20% asbestos) – but what could they be? Could it be a mixture of plastic and asbestos? When exposed to fire, it smells like plastic, and the consistency is similar to hard foam, roughly speaking, but quite crumbly.

I have now found an image online that, in my opinion, could represent what the entire panel might look like: