The Sea to Summit Ultra-Sil Waterproof Backpack Cover keeps packs dry when hiking, backpacking, or traveling. Made of ultralight, waterproof 30D Ultra-Sil Cordura, its seamless construction ensures that the cover is waterproof. Keeper straps pull the pack cover tight across the pack harness, for secure coverage. The cover packs compactly into an included mini stuff sack that's attached to the cover so it doesn't get lost. The Sea to Summit Ultra-Sil Waterproof Backpack Cover is available in four sizes to cover a range of backpacks: X-Small fits packs from 15 to 30 liters, packs down to 4 x 2.5 inches, and weighs 2 ounces; Small fits packs from 30 to 50 liters, packs down to 4.25 x 2.75 inches, and weighs 3 ounces; Medium fits packs from 50 to 70 liters, packs down to 4.25 x 3 inches, and weighs 4 ounces; Large fits packs from 70 to 95 liters, packs down to 4.75 x 3 inches, and weighs 4.6 ounces. Backpack not included. Sea to Summit products are guaranteed against defects in materials or workmanship for the lifetime of the product.