Ozone, UV radiation, and oxidation are the enemies of rubber. They cause cracking, hardening, and eventual death. Butyl laughs at the sun.
You may not realize it, but you interact with Butyl rubber constantly. butyl material
Butyl is famously "air-tight." It has roughly 10% the permeability of natural rubber, making it the industry standard for inner tubes and airtight seals. Ozone, UV radiation, and oxidation are the enemies of rubber