A number of people in our group use silk. Some use it to put sheen and shimmer in felting. Some use it it add to wool batts to give them a visual lift and some spin silk and ply it with other things. Silk gives a luxury look and a beautiful visual highlight. Alan uses mulberry silk. Cathy uses banana fibre silk. Others use sari silk. There are all sorts of silks available. It pays to use the ones you can find to see what effects you can get. Craftsy gives some good tips for spinning silk.