Premium natural fabrics Silky-soft hypoallergenic merino wool lining and the finest organic cotton outer. 4 Season use Unlike other brand sleep sacks that come in either winter or summer weight/TOG rating, the Woolino 4 Season Sleep Bag can be used year-round. It’s suitable for room temperature 63-75F (17-24C). Because of merino’s unique ability to regulate body temperature, it helps keep your baby warm when it's cold and cool when it's hot. Grows with your baby It has a universal size so it can be used for babies 2 months up to 2 years old. For smaller babies, simply close the underarm snaps to adjust the fit. Toddler size fits from 2 - 4 years