SI Exxxtreme Sheets Pillow Case King Size Soft Rubber. This king-size pillow case, 20" x 36", made of soft rubber material is both super soft and 100% waterproof. Machine washable. Specifically designed to withstand your wildest bedroom play. Can be used with all types of lubricants, including oil-based. Constructed from extra-soft rubber they can be used for sleep as well as play!