From the Sinew guide on the net........Imitation sinew, or fake sinew is made from man made fibers such as polypropylene, polyester, and nylon. That ,"and nylon" would be enough for me not to use it as a bow string. Probably the reason Flintnp17 got so much stretch when he used it. Better off with B50,B55,or FF, linen, flax, but that is your call.