Silk is a natural protein fiber produced by the larvae of a moth. It is the only natural filament fiber — a filament is a long fiber and is often manufactured. Long fibers yield smooth, strong, fabrics. That’s why filament fiber is valued in textiles, and silk remains among the best. Silk is one of the oldest textiles originating in China and contributed to the beginning of trade. It’s renewable and biodegradable. While the production process may use more energy and water than some of the other natural fibers, it remains one of the most luxurious natural fibers.