Description from website: Made to wear over pj’s, organic baby sleep sacks eliminate the need for unsafe loose blankets in the crib. They’re crafted from lightweight breathable 100% organic cotton muslin for maximum airflow to reduce the risk of overheating. Our sleeping bag is sized to be extra-long so your little has more room to wiggle and sleep comfortably. Plus, the convenient inverted bottom zipper makes nighttime or naptime diaper changes a breeze. Our organic baby sleep sacks are consciously made with quality + sustainability in mind, and manufactured according to the strictest ecological, social, and processing standards 1.0 TOG. Wear over pajamas; can also be layered with warmer sleepwear in cooler temperatures.