The Big-Pak is a transparent and regenerable dehydrating cartridge. The Big-Pak contains 45 Grams of blue "Indicating" Silica Gel Desiccant. The Pak will turn from blue to pink when it can no longer pick-up more moisture. The Big-Pak will remove the moisture (and thus prevent corrosion) in a sealed 3 cubic ft. area. The Big-Pak can be regenerated hundreds and hundreds of times in the microwave. Good for large ammo cans, gun safes, tool boxes Etc.