Sun Shade Sails block up to 90% of harmful UVA and UVB rays with its high density polyethylene fabric. The UV stabilized shade sail is durable, yet breathable, allowing rain to pass through without collecting or pooling on top of the sail. Perfect for decks, patios, pool and play areas, picnic areas, parks, gazebos and more.Depending on availability, this Sun Shade Sail may be offered in different fabric weights listed as GSM (grams per square meter). A shade sail using a 230 gsm fabric will be a more densely knitted fabric than a 160 gsm fabric. The denser the fabric, the higher the UV protection.