DACRON Polyester is today's "classic" sailcloth fiber. It is often called by the Dupont trade name DACRON® although there are other suppliers of polyester yarn used in sailcloth. Polyester is widely used for its combination of reasonably low stretch, good strength, low cost and durability. Because it can be heated and shrunk during weaving to form a tight, stable woven cloth, polyester woven sailcloth remains a good choice for cruising sails and casual racing sails.

IMPORTANT TERMS DEFINED
Breaking Strength is the load required to break a fiber of specific weight (in denier.) Used primarily as a reference for measuring the effects of flex, sunlight and chemical attack on the ultimate strength of sailcloth over time.

Denier is the weight in grams for 9000 meters of a given yarn. A higher denier signifies a heavier fiber.

Fill fibers are large, straight horizontal fibers around which are woven vertical "warp" fibers (right.) This close-up shows large, straight horizontal "fill" fibers around which are woven vertical "warp" fibers.

Flex Strength is the ability of a fiber to retain its strength after being folded back and forth. Flex strength is commonly expressed as grams of load per unit of stretch for a certain amount of fiber weight. The higher the initial modulus the less the fiber will stretch.

Initial Modulus describes the material's inherent ability to resist stretch. Initial modulus is usually expressed as grams of load per unit of stretch for a certain amount of fiber weight. The higher the initial modulus the less the fiber will stretch.

UV Resistance measures the effect of sunlight on sailcloth. UV resistance is usually expressed as the time it would take for a material exposed to Florida sunlight to loose half of it's breaking strength.