Zowaysoon Adjustable Rock Climbing Helmet Outdoor Helmet for Caving Riding Cycling 1. Max head circumference: 24.4 inch; Minimum head circumference: 20.4 inch; Inner shell Material: imported black EPS 2. The ventilation slats in the top of the helmet breath correctly and the headlamp clasp-things on the front and back are a really nice feature. 3. The chin strap and buckles are placed just right so that nothing rubs uncomfortably on my face, jaw, chin, etc. 4. The helmet is pretty comfortable and ridge, really light, sturdy and very portable , its fits perfect when you adjust the straps and twist the knob in the back. 5. Easy release for when you remove it, you can use it to fine tune a tight fit on your head, Straps are easy to adjust and are soft not to bite into your neck. Extremely light, extremely comfortable, breezy, easy adjustments.