Mine came from Pine Hollow Longbows. It's the only place I could find it listed as FF (except maybe Amazon), though I'm sure the material is sold elsewhere (like Lancaster Archery) under different brand names. It has sooo much less stretch than Dacron, and is much lighter per strength. I haven't tested, but I read in TBB 2 that FF is ~55# strength per strand, and B-50 is ~30# strength per strand, and that's what I go by.