Full-Size Elastic Crib Sheet for a 4" - 6" Mattress 6 units per carton - color: White. All Portable Play Yard Style Cribs and all Portable / Compact Size Cribs with a 1" - 4" Mattress. 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.