I have a dogbane string that is holding up pretty good for me right now. I've also have had luck with hemp, but it's hit or miss with the stuff I can find locally on how consistent the strength is, so they end up over built and thick. I also like squirrel rawhide, it's some tough stuff! Takes me 3 squirrels for a string, cut them in a big circle and spiral in to get a long enough length, then twist the 3 plies together. My next goal is to build a sinew string, but haven't tackled that yet, but I know others seem to like them.