How to wash waterproof mattress protectors start by checking the care label for specific instructions. Most protectors can be machine-washed on a gentle cycle with cold water. Use mild detergent to avoid damaging the waterproof layer. It's best to avoid fabric softeners as they can compromise the protector's effectiveness. If the protector is heavily soiled, you can spot clean it before washing. After washing, air-dry it by laying it flat or hanging it to avoid shrinkage, and never place it in a dryer unless the label explicitly allows it. Regular cleaning will help maintain its waterproofing and extend its lifespan.