These hats are sized properly for infants, toddlers, kids, and adults! Not only that, they are lightweight, durable, and easy to pack and travel with. The front is made of light weight foam while the side and back panels are mesh netting and breathable. A classic snapback closure offers flexible size adjustments to reach the perfect fit. Small/baby: 3m - 18m (45cm) Medium/toddler: 18m - 4yrs (49cm) Large/kid: 4yrs+ (53cm) Adult: one size These measurements are with the snapback all the way closed. Please allow an extra 2cm-3cm for the adjustment.