The two-way zipper makes diaper changes a breeze. Snug Sleep Sack 0-3 Months: the original Arms-Up swaddle, has controlled resistance, ensuring ideal Arms-Up snug fit across the torso to support baby's self-soothing, with no loose layers to kick off during sleep. Light Weight Sleep Sack: the newborn swaddle is made with a single layer of jersey fabric to reduce risk of overheating. This 1.0 tog sleep sack is ideal for MODERATE room temperatures between 68°F & 75°F. Layer underneath for ideal temperature regulation. Machine Washable.