Mamoru-kun Waterproof & Anti-mite Sheet - Family Size This is a waterproof sheet that is dryer-safe. You can protect your mattress with just this one sheet, eliminating the need for a waterproof mattress protector. I ordered the wrong size and, after washing it once, I stored it for a long time without using it. If anyone is looking for one! Although it is unused, please consider purchasing only if you understand that it is a used item.