Why would you need a rain cover when the Eberlestock backpacks are made from waterproof NT1 fabric? If your going out on an extended trip or if an unforcasted driving rain suprises you, you'll appreciate having a rain cover along. Or maybe you'll be bivving your pack. Its sized to go over the X1A1 backpack and is fastened with and agressive elastic edging that pulls tight around the pack. Better safe than sorry. 7oz. Reversible Blaze Orange / Hardwoods.