|kevlar vs. dacron
year 1: same speed
year 2 - 5: the dacron stretches faster, the draft moves aft, and as the wind picks up the sail is slower (still fast in light air)
year 6: the kevlar falls apart, which is very slow.
Dacron will last for years and years, but is no longer fast after year 1 when the wind picks up
if you are semi-serious about racing, buy kevlar - there is not much difference in price