UV- radiation: In the presence of oxygen, UV-radiation can cause a breakdown of the polymer chains.
Ozone: Attacks from ozone on unsaturated polymers (e.g. natural rubber) under stress, causes characteristic cracks.
Water: Absorption of water at elevated temperatures causes hydrolysis of certain groups in a polymer chain (e.g. urethane and ester groups). Hydrolysis weakens the polymer since the backbone structure is altered.