Mohair- is a silk like fiber that comes from goat hair, some of its characteristics are similar to wool. Mohair is very resilient, durable and is often known for its high sheen. Several carpets blend in this material because of the benefits noted above. This is very warm in winter and cool in summer which makes it popular for family rooms. Like wool it is flame resistant and does not bend permanently easily or wear. The main downside is the cost, this is considered a luxury material.
Silk- this is a material that can be woven into textiles. Silk comes from the silk worm and is extremely strong. As a face fiber (the side you see)it does not work well for carpeting but is sometimes used in area rugs. Some expensive rugs can have a silk backing woven in.
Regenerated fibers- These fibers are commonly referred to a synthetic because they are made from similar machines as synthetic fibers. They also carry some of the same characteristics like degrading from sunlight easily. They also can can suffer from browning and shrinkage if not careful with cleaning solutions and processes.