Cloth
UV strip
A sacrificial cover on a furling headsail that protects the rolled sail from sunlight.
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A UV strip is the sacrificial cover sewn along the exposed edge of a furling headsail. When the sail is rolled, most of the cloth is hidden inside the roll, but one strip remains outside in the sun. That strip is made to take the damage so the working sailcloth does not.
It usually runs along the leech and foot, because those are the edges left outside when a genoa or jib is furled. The material may be acrylic, polyester cover cloth, or another UV-resistant fabric. It adds weight, especially high on the leech, but it saves the sail from constant sunlight.
The strip should be on the side that ends up outside when the sail is furled. If the furler rolls the opposite way, the cover is hidden and the sailcloth is exposed, which defeats the whole point.