Velvet today is usually made from synthetic and natural fibers, but it was originally made from silk. Pure silk velvet is rare today, as it’s extremely expensive. Most velvet that is marketed as silk velvet combines both silk and rayon. Synthetic velvet can be made from polyester, nylon, viscose, or rayon.
There are several different Holland velvet fabric types, as the fabric can be woven from a variety of different materials using a variety of methods.
http://www.aochentextile.com/velvet-fabric/holland-velvet-fabric/