The fabric is bamboo mesh and regular mesh. It can be opened from both the top and bottom, making diaper changes easy. The size is M. According to the official website, size S is for 0-3 months, but it runs quite small. My daughter, who was born at 2950g, wore it from newborn to 3 months. She slept for 3-4 hours when she was a newborn wearing this, and around 7 hours when she was 3 months old. It's a fabric that can be worn in the summer, but I was also using it now that it's gotten cold. It doesn't trap heat, which is great (*^^*) There are no milk stains or pilling. Magic Swaddle Swaddle Up Nekurumi