These are great quality, very nice and thick. In the winter it might add good warmth as a layer for very cold weather. For the spring/summer they are perfect alone with shorts. Personally I don't like flimsy onesies worn alone so I love that these aren't too thin. The designs are adorable. My baby is about 17 pounds and the 6-9 months fit great with some room to grow (he is almost six months). Very happy with my purchase.