The protein fibers are formed by natural animal sources through condensation of a-amino acids to form repeating polyamide units with various substituents on the a-carbon atom. The sequence and type of amino acids making up the individual protein chains contribute to the overall properties of the resultant fiber. Two major classes of natural protein fibers exist and include
- Keratin (hair or fur) and
- Secreted (insect) fibers.
In general, protein fibers are fibers of moderate strength, resiliency, and elasticity. They have excellent moisture absorbency and transport characteristics. They do not build up static charge. While they have fair acid resistance, they are readily attacked by bases and oxidizing agents. They tend to yellow in sun Iight due to oxidative attack.