The Matrix is the first equestrian helmet made with the NEW PATENTED CONE HEAD Technology. Traditional helmets absorb the energy from an impact down thru the skull and into the neck. The Matrix with PATENTED Cone Head Technology has two layers of foam with the second layer made of formed cone shaped foam that disperses the energy laterally away from the skull and neck. It was developed in Australia by a physicist and has received worldwide acclaim. the Matrix also boast"s Devon-Aires famous dial fit retention system that allows for a custom, comfortable fit with the turn of a dial. Low profile and extremely light weight. Generous large vents for maximum air circulation can be closed during wet and cold weather to maintain body temperature. Fully adjustable nylon 4 point harness with easy quick release snap buckle. Removable cushioned head liner for easy care and washing. SEI Certified to ASTM F-1163-04a. Black or Charcoal Grey. Small fits 20 1/2" - 22 1/8" (6 1/2- 7); Medium fits 21 1/4"- 22 3/4" ( 6 3/4- 7 1/4); Large fits- 23 1/8"- 24 3/4" ( 7 3/8- 7 7/8).