Camera Light Seal Foam is also called a Light Seal and it is located inside the back cover of camera.
It is to prevent from light leaks.
Japanese camera manufactures have used this materials for anti-reflection long time. Therefore, this is best anti-reflection materials for cameras and Binoculars. Made in Japan.
Refer to "Let’s Try! - Repair and Maintenance of Cameras by Michio Ozeki (Author)" Amazon paperback
It is to prevent from light leaks. Japanese camera manufactures have used this materials for anti-reflection long time. Therefore, this is best anti-reflection materials for cameras and Binoculars. Made in Japan