Assuming you have a flemish style string find one of the tag ends near an end loop and pull it out. Take a decent pair of scissors and attempt to cut off the tag. If you can cut the tag after an attempt or two(this depends on how crappy your scissors are)then your current string material is B-50. If after several attempts you are unable to cut the string and the string material continually mashes sideways then you have some form of fast flight or other high performance material. You can also try this test. First measure and record your brace height. Lay the bow in your lap with the back of the bow towards the floor and the belly(not yours)facing the ceiling. Towards the ends of both limbs wrap your hands around both the string and then limb and lean over the bow while placing the string across you upper abdomen sternum area. Apply pressure to the ends of the limbs while exerting pressure with your abdomen/sternum area onto the string. If the string is B-50 there is going to be some change in your brace height. If the string is some type of fast flite or other high performance material there will be no change of any sort. Pictures to follow soon.