Protecting Your Head On A Bicycle

Road
The original bike helmets were made for bicycling on roads and road racing. As they have evolved, they mostly had an elongated shape, always with vents, and are usually made with EPS foam covered by a thin plastic shell. These are the most-used helmets in the world, and millions of them are sold every year.

Commuter
The term coined by Bell in 2004 when they introduced their Metro model. It has come to mean a helmet with a rounded shape, rather than the elongated road style. Has vents, and is usually made with EPS foam covered by a thin plastic shell. It sometimes has accessories such as mirrors, winter ear flaps and rear blinkers that are useful for commuting.

Mountain Bike Racing
A lightweight motorcycle-style helmet, usually with a chinbar to give some facial protection. Used in off-road downhill races, usually on wooded terrain with rough courses. Generally has vents, and is made of EPS foam with either a thin plastic shell or a thicker one made of either plastic or a composite material such as fiberglass or carbon fiber. One of the few choices for road riders who want facial protection but must have vents. The best are certified to the ASTM F1952 Downhill Racing Helmet standard.

BMX
A lightweight to full weight motorcycle-style helmet. Some are just motorcycle helmets sold to BMX (Bicycle Moto-Cross) riders. Always has a chinbar for facial protection, and usually has a big, squared off visor bolted to the helmet. Made of EPS foam with a shell of plastic or composite material such as fiberglass or carbon fiber. Sometimes has vents, but usually small ones, since BMX races are usually short. Some are certified to the ASTM F 2032 BMX bicycle helmet standard, others to the more protective DOT motorcycle standard. Only the Snell M-2005 motorcycle standard requires impact energy management in the chinbar in the form of crushable foam.