H2O Moisture Absorbing Packets attract water vapor like a sponge, vastly out-performing Silica Gel and other standard desiccants by 1000%. Available in a variety of sizes to suit many applications, their unique design enables each packet to capture water on a microscopic level by bonding with the H2O molecules. Because of each packet's expansion properties an incredible amount of moisture is absorbed, preventing corrosion. Once activated, over time, the packet will become swollen, indicating replacement is required. Our 7"x 7" packets protect 20 cubic foot enclosures. This product is sold in a case of 10 units.