aden + anais cozy sleeping bags are four layers of muslin, making babies comfortably warm during cold, wintry nights. aden + anais sleeping bags are designed to be worn over a baby's pajamas, ensuring a safe night's sleep by eliminating loose crib blankets, which can be dangerous. Muslin's light, open weave allows a baby's body temperature to regulate itself naturally helping to prevent overheating. aden + anais sleeping bags offer the ultimate in breathability and softness, as the more the more you wash them, the softer they get. Each sleeping bag zips from the bottom, making diaper changes easy, and a strip of muslin over the zipper by baby's face provides extra comfort.