I use silk noil (rough silk fabric). If you get undyed noil and use epoxy, it dries almost clear (see through). I always stretch it with a rough jig I made with a 2x6 and a ratcheting trailer tie down. I stretch it before glue up and apply it under tension (for flatbows only so far). I have a theory that if it is applied under tension, it may help support the back of the bow. Based on mention in the Bowyers Bible 1 of experiments done by Hickman with silk before WW2 and materials studies that suggest that silk/epoxy composites form a matrix similar to f****glass.
Just my 1/2 cent.
SB