Finally a long sleeved sleepsack for winter nights! I cannot understand why all the other sleepsacks out there are sleeveless, especially the ones intended for winter use. My baby's arms were always so cold last winter!This velour sleepsack is so soft and nice & thick (not like some of the thinner cotton/polyester blend velour material you sometimes see), it will keep your baby at least as (if not more) warm as in the polyester fleece Halo sleepsacks you usually see, only it is 100% organic cotton and therefore so much more soft, breathable, and comfortable, and chemical free! (Think about how much time your baby spends in these!) The body is generously sized and roomy and the arms are a bit more fitted (can comfortably fit a long-sleeved knit cotton pajama under it). The sizing is true to size (unlike Halo, which runs small). My 13 month old (who is 50th percentile height/weight) fits the 12-18 month with enough room to grow through this winter.I wish I had discovered these when my baby was younger (she is already 13 months) and wish I had never used those old polyester fleece ones you see everywhere! (Polyester makes baby sweaty.) Highly recommended. In case you are hesitating bc of the higher price compared to the cheap polyester fleece ones, think of it as buying a blanket (except it covers BOTH sides of the body!) that you will use every night - it's very reasonable for a blanket that will give your baby warmth and a comfortable night's sleep all winter long!