The Ultra-Breathable Cover features a certified organic fabric quilted to a unique 3D spacer material and is designed to maximize airflow around the baby. While we strongly encourage parents to put their babies to sleep on their backs in accordance with CPSC recommendations, this breathable surface adds an additional layer of safety should the baby turn face-down into a compromised sleep position. It also dissipates heat and moisture for a more comfortable sleep. Fits nearly all 6” standard size crib mattresses.