FF type materials aren't nearly as elastic as dacron, so they put more of the bow's energy behind the arrow rather than waste it in string ocillation (one theory). Another is they are so much stronger than dacron that you can make a string with fewer strands, therefore lighter, and pick up speed.

Personally, a few fps doesn't mean squat to me. I like the increased durability, lack of stretch/creep, and reduced handshock they offer. I've been shooting the same bow for 10-12 years now--LOTS of tournament shooting, practice, playing, and even a shot here and there hunting. It's never had a dacron string on it, and she shoots as good today as the day I got it--and I'm the type that can tear up an anvil with a cotton ball.

Funny thing is, if a bow fails and has anything other than a dacron string on it, usually the string gets the blame. When one fails with a different type string, something else is to blame. I've had and seen a LOT more bows fail with a dacron string. The only two I know of personally were old bows (not made for FF) that the tips sawn off by unpadded, small diameter strings.

Won't hurt anything to use dacron on a FF rated bow, but I don't see the point in it myself.

Chad