These hats are sized properly for infants, toddlers, kids, and adults! 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.