The Lullaby Earth Breathe Safe 2-Stage Breathable Crib Mattress maximizes airflow and supports growing little ones. The hypoallergenic mattress The mattress's lightweight core supports baby's developing muscles and bones yet allows for quick, easy sheet changes. The unique dual-stage design offers a firm side for infants and a medium-firm side for toddlers, so it grows right alongside your little one. And its reinforced edges are an added safety bonus for rambunctious, bouncing toddlers.