Kevlar sails are fine on furlers, with a couple of caveats. And actually, the best way to stow them, is to roll them up, just like one does on a furler. Only it's usually done at the Yacht Club, on a patch of grass, or clean section of the parking lot. And then they're slipped into their (soft) storage
The catches to storing them on furlers are:
- Their vulnerability to UV. So they need Good UV strips affixed to them, & or, full covers.
- They can be more prone to damage from chafe, if not built with their outer layers designed to resist such. As if they're just Kevlar material or yarns, laminated in between 2 layers of Mylar, then they tend to be kind of fragile. Mylar not being high on the abrasion resistance scale.
So that anything which rubs on them can be problematic.
And even with good UV covers, if they don't have that built in abrasion resistance, then when stowed on a furler long term, the different layers in the wrap on the headstay (furler) can chafe against one another.