Halo SleepSack Micro-Fleece Wearable Blanket, Baby Blue. 100% polyester Use over regular sleepwear to take the place of loose blankets. Unzips from the bottom for easy diaper changes. Generous sack design allows room for kicking, but cannot be kicked off so baby stays warm all night. Sleeveless design reduces the risk of overheating. Used by hospitals as their product of choice for teaching parents safe sleep practices.