Ultralight, low profile helmet with large vents provides superior ventilation for a cooler, more comfortable ride. Key features include: Low profile Durable, lightweight construction Six mesh covered vents DialFit system FlipFold removable washable headliner* with Air-Channel technology ASTM/SEI-certified SMALL Hat Size 6 5/8 - 7 Head Size 20 3/4" - 22" MEDIUM Hat Size 7 - 7 1/4 Head Size 22 - 22 3/4" LARGE Hat Size 7 1/4 - 7 3/8 Head Size 22 3/4" - 23 1/8" XLARGE Hat Size 7 3/8 - 7 3/4 Head Size 23 1/8" - 24 3/8"