Polyester sailcloth is amazingly strong and durable stuff, often completing trips around the world or decades of weekend sailing. Its Achilles heel is the sun. After just 2-3 years in the sun, depending on the latitude, it becomes so rotted by UV that its little stronger than a cotton bed sheet. Mainsails are safely bundled under a Sunbrella cover. Nylon Spinnakers are bagged and stored below. Genoas, on the other hand, remain furled on the headstay, often year round, with the last 12 inches of the leach and foot continuously exposed.