Protein fibers have good moisture absorbency and transport properties while not building up static charge. They are fairly acid resistant but readily attacked by bases and oxidizing agents, and tend to yellow in sunlight. Silk fibers are produced by the Bombyx mori silkworm through a process where the silkworm spins a cocoon made of silk protein strands, which are then harvested and processed into silk fibers. Wool fibers are obtained from sheep and other animals and have crimped, elastic fibers that grow in clusters, giving wool fabrics bulk and the ability to retain heat. Angora fiber comes from the coat of the Angora rabbit and is known for its softness, thin fibers, and fluffy texture.