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 & softness, as the more the more you wash them, the softer they get. Each sleeping bag zips from the bottom, making nappy changes easy, & a strip of muslin over the zipper by baby's face provides extra comfort.