Bike helmets consist of helmet liners, shells and straps. Bike helmet liners are usually made of Expanded Polystyrene (EPS) foam, Expanded PolyPropylene (EPP) or Expanded Polyurethane (EPU or PU). The shell for cheaper helmets is stamped PET, ABS, polycarbonate
plastic or other plastic, while some helmet shells may include layers of fiberglass or kevlar. Helmet strap parts are made of nylon or polypropylene.
The liner is the most essential part of your helmet: it is the foam layer that absorbs the energy and shock of an impact. Bike helmet liners are made from Expanded Polystyrene (EPS).
Cheaper helmets – which make up most of helmet sales worldwide – are made using standard techniques. Granules of EPS foam are placed in molds and expanded using pressure and steam. This technique is mainly used in China, but there are many American and European helmet manufacturers that also use this technique.
More top-end helmets use materials such as polypropylene, nylon, and metal mesh to reinforce the internal structure of the helmet. This reinforcement is typically buried within the foam, so it is not noticeable to the wearer, but it is vital for helmets with larger air vents to have this reinforcement to stop them from breaking on impact.
EPS foam can be made with different densities to manage impacts, with softer layer to cushion your head in lesser impacts and harder layers that can handle the bad hits. In the more expensive helmets, the density may vary around the vents to ensure that they meet impact standards.
There are a few other types of foam that have started to emerge in the bike helmet market, such as Expanded Polyurethane (EPU), Expanded Polypropylene (EPP), and rate-sensitive slow rebound foam. Each of these foams also has a different manufacturing technique.
The shells on inexpensive helmets are normally stamped PET plastic, which is the same material that water bottles are made from. This plastic shell is typically glued to the liner and taped around the edges to give it a smoother appearance. However, some cheap models do not use glue or tape.
More expensive bike helmets include the shell in the mold, so the liner expands into the shell. These shells are made from polycarbonate plastic or other high-quality plastic, as these can withstand the heat in the molding process.
Some skate-style and bike helmets use ABS plastic, while some BMX bike helmets use composite shells that are made using layers of Kevlar fiber and epoxy or fiberglass.
The straps on a bike helmets are normally made from polypropylene or nylon. While they all look fairly similar, they vary a lot in surface finish, fabric, weave, and other characteristics.
Bike helmets that have glued-on shells have the straps added to the liner and then the shell is glued onto the liner. When the helmet is molded into the shell, the straps are added onto the helmet after it is removed from the mold and is attached with an anchor. Bike helmets that have hard shells typically have the straps attached with rivets to the shell.
The buckle is an important part of the helmet and is the piece that ensures that the straps keep the helmet on your head in a collision. Helmet buckles are normally made from nylon or plastic with a side pinch release system. Some helmets use a metal D-ring buckle system.
Bike helmets which are made with ring-fit systems are fitted with adjustable rings inside. Helmets with fitting pads normally get a hook-and-loop mount glued into it, and then the pads are added.
Some cheaper helmets have these pads glued straight onto the liner’s interior. Other have a plastic liner or interior cloth applied.
The main impact-absorbing part of a bike helmet is the inner liner, which is typically made from EPS foam. Their energy absorption abilities are omnidirectional, so they can absorb energy from any direction.
Looking at what your helmet is made from can make the difference between life and death when cycling on roads. Be sure that you buy the highest quality helmet that your budget will allow. Your helmet is the one piece of cycling equipment that can literally save your life.