The 2-piece safe asleep® Baby Sleeping Bag set consists of the Air Jersey sleeping bag and a cotton romper bag. The sleeping bag is equipped with the AIR balance system, which acts as a natural air conditioner. The high breathability and rapid moisture absorption and release create a healthy sleeping environment. Size is crucial when choosing a baby sleeping bag. If the sleeping bag is too big, your baby gets cold more easily and can slip too far down. If the sleeping bag is too small, your child feels constricted and cannot stretch their legs properly. When choosing the perfect sleeping bag size, the following rule of thumb applies "Body length-head length + 10cm." The extra 10cm gives your baby enough freedom of movement and room to grow. It's just as important to choose the right TOG value and thickness of the sleeping bag to match the temperature of the room.