Ely's & Co.Waterproof Pack n Play/Portable Crib Sheet and Mattress Pad Cover Our Waterproof Pack n Play sheet is lined throughout with TPU especially designed with no seams to prevent leakage, so no mattress pad cover, mattress liner or mattress protector is necessary. Clean up is a breeze and your portable crib and pack & play mattress and mat are fully protected. Our Pack n Play Portable Crib Sheet Sets are composed of light, soft and breathable fabric. Made from 100% high quality Jersey knit cotton, babies love our Pack n Play sheets, as they offer a soft, welcoming texture that lulls them into restful sleep.