These are Muji brand kids' pajamas. They're made of a slightly thick cut-and-sew fabric, 100% cotton, which feels very soft against the skin and is also stretchy. They were also good for practicing buttoning. The price was a bit high, but my child basically wore this series of pajamas. Unfortunately, they are now discontinued, and the pajamas without side seams seem to be double gauze now. They were a good product in terms of stretch, warmth, and feel, so I wish they would bring them back. These were purchased for a trip home (stored at my parents' house), and the number of times they were worn is relatively few. Please consider them. Sleeve Length...Long sleeve Season...Winter, Autumn