2PCS AYAMAYA Waterproof Pack Rain Cover (35-40 L) Backpack Rucksack Book Bag Ultralight Raincover Dust Snow Proof Protect your pack and its contents from downpours with the Ultra-Silm Pack Rain Cover. A great way to keep the rain out of your pack. This pack cover uses a "no seam" construction for complete waterproofness This a raincover for a day pack or book bag. Fits most packs 35-40L. The Rain Cover also includes elastic binding around the edges for a snug fit around your backpack. Weighing in at only 2 ounces, the cover won't weigh you down as you slog through the mud. In fact, it probably weighs less than the water you'd otherwise take on during the average gully-washer.