This is a large, lightweight, waterproof stuff sack designed to fit inside a backpack. It's made of a lightweight waterproof material and is designed to fit inside a backpack. The oval bottom makes it easier to fit into the bottom of a backpack. The opening is temporarily secured with Velcro, then rolled up and secured with a buckle. Seam-sealed. While it's generally recommended to individually waterproof items you don't want to get wet inside your pack, using an inner sack provides even more peace of mind. This is essential equipment for river trekking. I purchased this about 10 years ago and have used it about 5 times, but it has never gotten wet. There is no hydrolysis, but it is a used item, so please understand this before purchasing. No claims and no returns accepted. The photos look blue, but the actual color is purple. It will be folded and shipped in the smallest possible packaging. 【Material】 30D nylon ripstop, silicone water repellent/PU waterproof coating 【Size】 Height 850 x Width 445 Fits perfectly in a 50-liter class backpack.