From Reima website: This wool all-in-one, can be worn indoors or as a mid-layer. The Merino wool feels soft against skin and is ideal for regulating your little one's temperature. Brushed interior for extra warmth. This breathable toddlers' woollen Reima all-in-one is a great mid-layer underneath outerwear. Its interior is brushed soft, so it feels super nice against skin. The popular style comes with comfortable ribbed cuffs. A full-length zipper makes putting the piece on easy and the chin guard protects delicate necks from the zip. For added comfort, all the seams on this all-in-one have a thin, flat construction that doesn't chafe. ** in my experience, Reima runs about one size big**