Blue Bird Print Cotton Sleep Sack Small HALO Safe and Snug Sleep: Explore Our Baby Sleep Sacks Collection WildBird Estate Blue Signature Sleep Sack (0.5 TOG) Cosoco Kids Singapore Halo Neutral Cotton SleepSack in Multi Dot (Size Small) Overstock. HALO SleepSack is the original wearable blanket for safe sleep, designed to help babies get better, longer sleep. As the next step after swaddles, it ensures a smooth transition with its zipper for easy diaper changes and a roomy, extra long sack that supports hip health and extends use. Crafted from breathable 100% cotton fabric, it offers cozy quality comfort your baby will love.