Shade Sails feature unique Commercial Grade high density polyethylene knitted fabric specially designed to breathe and keep you cooler and more comfortable in hot weather. This state of the art material contains Heavy Duty 280gms/sqm cloth fabric and blocks up to 90% of the sun’s harmful UV rays yet remains totally unaffected by moisture and natural temperature extremes. And because this fabric is knitted, not woven, it won't tear or fray. The perimeter of each sail is designed with a gentle curve inwards towards the center of the sail to control fabric tension. Shade Sails have reinforced webbing around the perimeter and a stainless steel "Delta" ring at each corner. Therefore, when tension is placed on the ShadeSail, the fabric will not wrinkle.