Coghlan’s Lightweight Dry Bag – 25L (10” x 20”):

Made from lightweight 40D rip-stop nylon, these pack down better than typical dry bag fabrics. They also have fully taped, waterproof seams. They’re ideal for use while backpacking, for adventure travel or for water sports but are not intended to be submerged underwater.
10” x 20” (26 cm x 52 cm)