The Oxford baby perfect comfort 2-stage crib mattress is a high-quality, durable crib-to-toddler mattress with a lightweight 5.5" H polyester core – thousands of tiny air chambers between the compressed fibers allow air to flow freely for better breathability and a fresher mattress. Your infant or toddler can sleep on either side of this firm mattress, making for a more restful night's sleep. The firm side is for infants to 12 months as recommended by pediatricians. After 12 months, the toddler side has a thick extra layer of padding for a more comfortable sleep surface. The mattress is lightweight and is easy to clean.