Bamboo blend fabric and a perfectly light weight for year-round wear. Measurements are from FLAT fabric. Your head should measure slightly larger than the fabric or it will be too big. Many adults choose to size down.

Circumference: Stretches appx 3"
Newborn: 13" before stretch
3-12 Months: 15" before stretch
1-3 Years: 17" before stretch
4-12 Years: 19" before stretch

Youth/Adult Small: 21"
Adult: 22" before stretch