European camera makers designed their backs so that they would block light without the need for other materials.
Some camera makers used yarn as a light blocking material for the top deck.
In general, you'll rarely find a European camera with foam. Even today, you can count on one hand the number of German cameras that use foam to block light.
Japanese camera makers began to use foam in the 1960s.
The most difficult part of old foam is removing it. If it's beginning to crumble, I would stop using the camera until you can get it replaced. The reason is that you don't want any chunks or tiny pieces to get into the mechanisms.