Bicycle Helmet Terms and Definitions
Note: we also have a page up with longer definitions of helmet types.
BMX helmet: Helmet for use in Bicycle MotoCross events. Most are hard shell, full coverage motorcycle-style helmets with chinbars and few if any vents.
Bridge: The part of a helmet running crosswise between vents.
Buckle: The strap fastener. Most common is the Fastex style buckle from ITW Nexis, a plastic piece that opens by pinching the sides.
Bug net: Mesh or net placed in vents to keep insects out, usually found only in the front vents. Mostly found on helmets made for the European market.
Cam lock: Strap adjusters that lock with a cam by turning a dial or flipping a lever. The cam pinches the strap when its thicker edge is engaged.
Carbon fiber (carbon for short): A trendy, very high strength fiber replacing the glass fibers in a helmet shell. Must be saturated with epoxy and encased in the shell to provide strength. Lighter than glass fiber and may permit a thinner shell. Used as an internal reinforcement, carbon fiber's strength may permit opening up larger vents. Expensive, particularly as it became scarce during 2006.
Chinbar: A piece of helmet shell that extends down and around the chin to offer some facial protection. If the helmet meets the Snell M-2005 motorcycle helmet standard the chinbar must have impact foam, but most BMX or downhill helmets do not.
Chrono helmet: A very smooth aerodynamic helmet for time trials and track racing. Usually teardrop shaped. Not suitable for street use.
D-ring buckle: A very strong, reliable buckle made by sewing to D-shaped rings at the end of the strap and threading the other strap end through them. Normally made of stainless steel.
Downhill mountain bike helmet: A helmet made for downhill mountain bike racing The ones that meet the ASTM F1952 standard have extended coverage and better impact protection than a standard bike helmet. Most have vents and chinbars, but the chinbars often have no impact foam. Some chinbars are detachable.
Dual certified: A skate style helmet liner is certified to both the CPSC bicycle helmet standard and the ASTM F 1492 skateboard standard, providing protection in both hard bicycle impacts and multiple skateboard impacts. We have a list of dual-certified helmets.
Dual density: A helmet liner that has two layers, one stiffer and denser than the other. Usually used to provide a soft landing for lesser impacts backed up by a stiffer layer to handle very hard impacts.
Flip-off visor: A visor that readily detaches from the helmet in a crash or when snagged on an overhangin limb.
Foam: The material used for the inner liner of a helmet, the part that actually manages impact energy. It may be stiff, crushable foam or squishy, rebounding foam. Our page on foams explains the many types.
Glued on shell: The process of attaching a thin plastic shell to a foam liner with glue.
Hard shell: Exterior surface of a helmet that is made of thick, hard plastic, fiberglass or other material. Resists point loading, so it disperses impacts from rounded or pointy objects over a larger surface.
Internal reinforcement: A plastic, nylon, carbon fiber or metal ring or other structure buried in the foam of a helmet to keep the foam from cracking when impacted. Permits opening up larger vents, but costs more to manufacture, so it is usually found on more expensive helmets.
Liner: The thick inner layer of a helmet that actually manages the impact energy, always made of some type of foam. The tuning of the foam characteristics to work with the vents and other elements of a helmet is the most critical part of helmet design.
Matte: A flat, not glossy surface finish.
Microshell: See thin shell below.
Molded in the shell: A maufacturing technique that expands the liner foam into a shell placed in the same mold to leave no voids and bond the shell to the liner. Requires a higher-quality shell such as polycarbonate that will not melt in the mold. More expensive than taping or gluing the shell, but can produce a stronger helmet or a helmet with more vents.
Motorcycle helmet: A thick, heavy, unvented helmet with a hard shell, full coverage and usually very good impact performance normally used by motorcycle riders. Most have chinbars. If they meet the Snell M-2005 motorcycle helmet standard the chinbar must have impact foam.
Mountain Bike helmet: A mostly artificial distinction for a helmet that is for off-road riding. Most are road helmets with visors added.
No-pinch buckle: A buckle with a pad or tab underneath to prevent pinching of skin when the buckle slides together. Particularly useful for toddler helmets and for seniors with loose skin under the chin.
Occipital stabilizer: a strap or other device at the rear of a helmet designed to come down below the lump (occiput) to grip and stabilize the helmet. Not tested for strength under any helmet standard, because it is "for comfort" and not considered part of the retention system. Will not hold the helmet on your head in a crash and does not substitute for careful strap adjustment.
Pad fit: A helmet that fits with internal fitting pads instead of an adjustable ring.
Polycarbonate: a high-quality shell plastic used for some bicycle helmets, particularly those that are molded in the shell. GE's Lexan and Bayer's Makrolon are particular brands.
Pony tail port: a rear opening in a helmet or occipital stabilizer that accommodates long hair gathered in a pony tail.
Rear fin: A piece of plastic that rises above a helmet shell in the rear, contributing nothing to safety and forming a potential snag point.
Ring fit: A helmet that fits by adjusting an internal ring. Works well for some heads but not for others where the ring must be tightened too much to achieve a stable fit.
Road helmet: A helmet designed for use by almost any bicycle rider, including those who ride on roads or paved trails.
Roost guard: A foam or other padded rim around the inside of a BMX helmet's chin bar and face opening to fill the gap between the helmet opening and the rider's face. It keeps out the dirt and gravel thrown up by the wheels of riders just ahead. The dirt is known as "roost," probably coming from rooster tail, the term for the plume of water thrown up by a powerful boat propeller.
Shell: The outer surface of a helmet, usually made of plastic, fiberglass or other fiber-reinforced plastic.
Skate helmet: A helmet designed for roller skating or skateboarding, typically made with a hard ABS shell and small vents. The classic skate style has lower rear coverage. Roller skating or inline skating require a bicycle helmet, so most are now certified to the CPSC bicycle helmet standard and are one-hit helmets with crushable foam liners. See skateboard below for true skateboard helmets.
Skateboard helmet: A helmet designed for skateboarding, typically made with a hard ABS shell and small vents. The classic skate style has lower rear coverage. For skateboarding a multi-impact helmet is required, so liners are typically made of EPP or squishy vinyl nitrate foam. Some are not designed for bicycle impacts, but for lesser falls. Those that are dual certified can handle both.
Snag point: A sharp projection on the shell of a helmet that risks snagging the impact surface in a crash and jerking the rider's neck.
Standards: Lab test protocols designed to prove that a helmet can manage impacts and has the necessary coverage and strap strength to perform well. Designers typically design to meet a standard but not exceed it by much. Bicycle helmets typically are certified to:
- CPSC: the legally-required standard for any bicycle helmet sold in the US.
- ASTM F 1952: downhill mountain bike racing standard requiring more coverage and more impact protection than CPSC.
- ASTM F 1492: ASTM skateboard standard requiring four hits in one spot and more coverage but less severe impact protection than CPSC.
- ASTM F 2032: BMX standard requiring more coverage than CPSC.
- EN 1078: European bicycle helmet standard requiring less impact protection than CPSC.
- DOT: US Dept. of Transportation motorcycle helmet standard requiring much more impact protection and coverage than CPSC, but sometimes met by BMX helmets.
- Snell M-2005: motorcycle helmet standard requiring much more impact protection than any other in this list, and the only one that requires that chinbars be able to manage impacts.
Strap anchors: The pieces at the end of the strap that sit at the surface of the helmet or just above the shell.
Tabbed buckle: a buckle with a tab behind it to prevent skin from being pinched when the buckle is closed.
Taped on shell: An inexpensive manufacturing technique where the shell is put on a liner and taped around the edges to hold it together. Usually requires more foam in a helmet than molding in the shell, and that can result in a more protective helmet with smaller vents.
Team model: A helmet made for a racing team sponsored at least in part by the helmet manufacturer.
Team graphics: Colors and usually complex graphics used on a team helmet.
Thin shell: Thin, tough plastic used as the outer shell of a helmet, and usually no thicker than a clear water bottle.
Time trial helmet: See chrono above.
Titanium: An expensive metal that is stronger than steel by weight but cannot save enough weight in a bicycle helmet to be anything but a marketing gimmick.
Toddler helmet: A helmet made for an infant or toddler aged one to five years.
Tri-glides: Strap side junctions that are placed just below the ear to bring the front and rear straps together.
Unobtanium: A promised new material or construction technique that has not been brought to the consumer market yet, and may never be.
Vents: Openings in the shell and liner of a helmet to let cooling air flow around the head.
Visor: A projection in front of a helmet to shade the eyes. Typically removable and hopefully separates easily from the helmet in case of impact to avoid snagging on the impact surface.
Woman Specific Design - WSD: a largely illusory term used to denote a helmet that is marketed to women in medium sizes with cosmetic differences such as pastel colors. A few actually do have pony tail ports.
This page was revised or reformatted on: February 22, 2019.