Delta Children's crib and toddler mattress is built with a firm polyester fiber core. This sturdy baby mattress features a high performance ThermoCool cover with waterproof backing helps create a cooler sleep environment. Square corners to help create a secure fit inside a crib or toddler bed, this crib and toddler mattress is the ideal choice for your growing child. The included fitted crib sheet keeps its softness, wash after wash.