Mountain bike helmets are made from polystyrene, which crushes easily on impact and absorbs energy, thereby protecting the skull. Unlike a motorbike helmet, they have air flow vents to keep the rider cool and usually a visor to protect the rider from sun glare or rain on the face.
Cycling helmets have to conform to certain safety standards, the Consumer Product Safety Commission or CPSC in the US and EN1078 in the EU. There are other more demanding standards such as the Snell BS-90, a specification for higher quality helmets but CPSC and EN1078 cover the vast majority of helmets sold.
Prices start from around $25 for a basic helmet with some air vents and a sun visor. These are often referred to as leisure cycling helmets and are fine for recreational off-road cycling at a moderate pace. So called performance mountain bike helmets, however, are far more expensive with prices ranging from $50 to $150 for multiple vents and specific design characteristics for long hard days in the saddle.
Look for certain design features when considering a helmet purchase:
* Number of vents and positioning on sides and rear of helmet. Additional vents increase air flow so choose a style that offers the most cooling power for the type of riding preferred.
* Sizes available. Cheaper helmets tend to be one-size only whereas more expensive models come in 3 and even 4 sizes suitable for riders with extra large heads.
* Fit adjustment mechanism. These differ by brand so look for a system that is easy to use and offers fit adjustment both laterally and vertically if possible. Always try on a helmet for perfect fit before purchase.
* Inner ring mechanism. Usually featured on higher end helmets, this allows greater customization of fit and added comfort.
* Removable and adjustable sun visor.
* Anti-pinch buckle on neck strap.
* Padding made from a breathable material such as Coolmax to soak up sweat, which should be easy to remove for washing.
* Weight. As with most mountain bike gear, the lighter the product the higher the cost but weight can be important for racing or for riding in hot countries.
* Easily adjustable straps for a perfect fit.
* Availability of spare parts, such as pads or inner ring systems which can wear out easily.