100% cotton knit fitted crib sheets with heavy-duty elastic. Mint - 6 Pak. All Full-Size Cribs with a 1" to 6" 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.