Many different kinds of low stretch string. Some are pure Dynema like D97. D97 plus is a blend of Dynema, 85 percent, and Vectran 15 percent. Some are 70 30, and thinner diameter than others with more string count to get the same thickness, or a thinner string if you like. Fishing line is basically the same thing. I have made strings from 50 lb test. They end up at about 20 strands, and when waxed ,and burnished make a tough long lasting string. Dry fires with ff string has destroyed it's share of glass recurve bows. It tears through the over lays ,and wedges in the glass limb. I had one 8 strand ff string start to tear through a white Oak once with no over lays. Caught it in time,cleaned it up ,and put bone tip over lays on it. I put the same string back on the bow,and now it is fine. It is your choice ,but for me bone tip over lays when using ff string. Other guys will tell you they having been shooting ff with no tip over lays with wood bows with no problems. Some guys are padding the loops ,and getting away with it. In the end it's your choice.