The durability of any material is determined by its resistance to the damaging effects of an influence such as extreme temperature, ultra-violet radiation, exposure to aggressive chemicals, stress cycles, etc. Durability is assessed by measuring an appropriate material property such as strength, modulus, etc., before and after exposure to one or more such influence for a period of time under prescribed conditions. A high level of property retention is consistent with high (good) durability. In this respect, the "lifetime" of a material may be identified with the time of exposure that results in a particular property remaining above a certain level.
All composite materials are durable inasmuch as they are water resistant, thermally stable and cannot rust.
In almost all applications, the durability of a composite material may be enhanced by imposing a conservative safety factor (2-4) on the design, and in many such cases additional durability may be achieved by the use of a protective coating and/or the incorporation of light stabilisers and antioxidants.