The eVac Dry Sack utilizes 70D lightweight nylon fabric for strength, in addition to eVent® waterproof fabric on the base to allow eVac-uation of air for compression. It's an excellent option for storing and compressing clothes and sleeping bags without the use of straps. Just pack the items in, roll the sack down, and push the air out to save valuable backpack space. They're an oval shape, making them perfect for sliding into the contours of your pack, plus all seams are double stitched and tape-sealed.