The Reasons As For The Change Of Rubber Sheetings
Rubber variety, used in different conditions, changes that have occurred are also different.
Hard brittle: Br's aging, aging of nitrile-butadiene rubber, styrene-butadiene rubber.
Crack: unsaturated rubbers ozone aging photo-aging, cracking, most shapes are not the same.
Moldy rubber aging biological organisms.
There is also: spots, cracks, whitening cream, powder spray, and so on.