Swaddle Up for Babies Who Sleep Well ✴︎S size (usable from birth) Fabric is recommended for summer to early autumn ✴︎M size (6-8.5 kg) Recommended for late autumn onwards, when it gets a little cooler For babies born in summer, this is a convenient set: Use the S size from birth, and then the M size (fabric is a little thicker) when the seasons change and it's time to step up. You don't have to worry about which one to buy, and you can use it right away! The M size has zippers on the hands, so you can take one hand out at a time.