I have not noticed any UV degradation on our 10 year old (cruising Dacron) Main. We don't have any lazy-jack system, always flake the Main, and religiously cover the sail, unless we come in late at night and will be leaving early morning. Cruising in the Tropics (well, Bahamas), however the Main and its cover are well washed & cleaned, then rolled and stored inside 6-8 months of the year. Both are holding up quite well. Cheers, John