100% cotton knit, zippered, fully enclosed, safety crib sheet. All Portable/Compact-Size Cribs with a 3"- 4" Mattress. 6 units per carton - color: White. Foundations® SafeFit™ Crib Sheets are designed to maximize safety through superior fitting. Recent studies show that a large number of child safety hazards are created by improper bedding on cribs. Appropriate fit and 100% cotton knit provides the ultimate in softness, durability, and safety.