Material: 6-layer cotton gauze, soft, cozy and breathable. Size: M: Length: 27.5, for 5-18 months babys; L: Length: 31.5, for 2-3 years babys; XL: Length: 35.5, for 3-5 years babys. (Recommended age and height in the size chart are for reference only.) Detachable sleeves for 4 seasons. Vest-Type sleep sack for summer, and long sleeves for spring and autumn. Generous sack design allows room for kicking, but cannot be kicked off so child stays warm all night. Comfortable: zip for easy dressing and diaper changes.