Hello IroquoisArcher, I don' t know much about the materials of bowstring construction, but the spec. on what they call their " S4 One Cam Bowstring" is that it is made of 450 Plus. I know that I want something more stretch resistant than the Zebra strings. I put on a Zebra (a new spare that I' ve had a long time) and it stretched an amazing amount in 30 shots or so.[:@]