The Lifenest sleep covers are zippered sheets designed for your baby's safety in mind. These are designed just for the Lifenest that is a highly breathable sleeping and ergonomic sleep positioner babies Lifenest is the most unique sleeping system since the invention of the mattress itself. About the sleep covers - a main 3D spacer mesh fabric. Two additional lateral mesh fabrics for ventilation channels. Four ribbons to secure the mattress to the crib slats. A lead free double slider YKK zipper. Available in 3 different colors white, pink and blue.