Helmets are made of two primary components: a hard outer shell that spreads impact force across a wide area, and a softer inner liner that crushes to absorb energy before it reaches your head. The specific materials vary depending on the helmet’s purpose, from a $30 bicycle helmet to a military-grade ballistic model, but that basic two-layer architecture remains consistent across nearly every type.
The Outer Shell
The outer shell is the first thing to contact a surface during an impact. Its job is to resist puncture and distribute force over a broad area so no single point on your skull takes the full hit. The four most common shell materials, from least to most expensive, are polycarbonate, fiberglass, carbon fiber, and aramid fiber (Kevlar).
Polycarbonate is the most widely used shell material in consumer helmets. It’s a thermoplastic that’s lightweight, reasonably impact-resistant, and cheap to manufacture through injection molding. Most budget and mid-range motorcycle helmets, ski helmets, and bicycle helmets use polycarbonate shells. The tradeoff is that it’s heavier and less impact-resistant than composite alternatives.
Fiberglass sits a step above polycarbonate. Fiberglass shells are both lighter and stronger, with better ability to absorb and dissipate impact energy. They’re made by layering glass fiber sheets with resin and curing them into shape. Many mid-to-premium motorcycle helmets use fiberglass or a fiberglass blend.
Carbon fiber is the lightest and strongest shell material available in consumer helmets. It offers superior impact resistance at a fraction of the weight, which is why it dominates in racing and high-performance helmets. The drawback is cost: a carbon fiber helmet can easily run two to three times the price of a polycarbonate equivalent.
Many premium helmets don’t use a single material. Manufacturers often layer fiberglass, carbon fiber, and aramid fiber together in a composite shell, tuning the layup to balance weight, strength, and cost.
The Impact-Absorbing Liner
Beneath the shell sits the component that does the most critical work: the energy-absorbing liner. In the vast majority of helmets, this is expanded polystyrene foam, commonly called EPS. It’s the same dense, white foam used in packaging, and it works by crushing on impact. As the foam compresses, it converts kinetic energy into deformation, slowing the acceleration your brain experiences from several hundred G-forces down to survivable levels.
EPS is effective but single-use. Once it crushes, it stays crushed and can’t absorb a second impact in the same spot. This is why helmets need to be replaced after any significant impact, even if the outer shell looks fine. Some newer helmets use expanded polypropylene (EPP) foam, which can partially recover its shape after compression, or dual-density EPS with softer and firmer layers tuned to handle both low-speed and high-speed impacts.
Rotational Protection Layers
A straight-on impact isn’t the only danger. Angled impacts cause the brain to rotate inside the skull, and that rotational motion is linked to concussions and more severe brain injuries. Several systems now address this with an additional layer between the shell and the EPS liner.
The most widely adopted is MIPS (Multi-directional Impact Protection System), developed in Sweden. A MIPS-equipped helmet includes a thin polycarbonate insert that sits against the inside of the foam liner. Small fabric pads between the insert and the foam create a low-friction interface. During an angled impact, this layer allows the helmet to slide roughly 10 to 15 millimeters relative to your head in the first critical milliseconds, reducing the rotational force transmitted to your brain. Early versions used a Teflon-coated interface; current designs rely on slippery fabric pads or stretch-fabric encased plates. MIPS is now found in hundreds of helmet models across cycling, skiing, motorcycling, and equestrian sports.
Comfort Liner and Fit Pads
The innermost layer, the one that touches your skin, is the comfort liner. It’s typically made from moisture-wicking fabrics like polyester or nylon mesh, often over thin foam padding. This layer handles sweat management, fit adjustment, and basic comfort. In most helmets, these pads are removable and washable. They play no meaningful role in impact protection.
Chin Straps and Retention Systems
A helmet that flies off your head during a crash offers zero protection, so the retention system matters. Most bicycle, climbing, and sport helmets use polyester or nylon webbing for chin straps. These synthetic materials are strong, lightweight, and resist stretching under load. The buckle is typically a simple plastic clip or, in motorcycle helmets, a double D-ring made from stainless steel or nickel-plated metal that locks the strap by threading it through two metal rings.
Military helmets are a notable exception. UK military helmets, for instance, use cotton webbing for chin straps rather than synthetics. The reason is that nylon and polyester can melt when exposed to extreme heat or flame, fusing to the skin. Cotton chars instead of melting, making it safer in combat environments where fire and explosions are possible.
Construction and Industrial Hard Hats
Hard hats used on construction sites and in factories follow a different design philosophy. They protect against falling objects and bumps rather than high-speed impacts, so they skip the thick EPS liner. Instead, a hard plastic shell connects to a suspension system of webbed straps inside that holds the shell away from your head, creating a gap that absorbs shock.
The two most common shell materials are high-density polyethylene (HDPE) and ABS plastic. HDPE is lighter, more flexible, resistant to chemicals and UV radiation, and cheaper to produce. It’s the standard choice for construction, logistics, and general maintenance. ABS plastic is more rigid and handles higher impacts better, making it the preferred material for heavy industry, mining, and manufacturing where falling objects are heavier or side impacts are more likely. ABS hard hats cost more and weigh slightly more, but they retain their shape under greater stress and handle heat better than HDPE.
Ballistic and Military Helmets
Military helmets are built to stop bullets and shrapnel, which demands entirely different materials. The two dominant options are aramid fibers (best known by the brand name Kevlar) and ultra-high-molecular-weight polyethylene, or UHMWPE.
Aramid fibers are woven into a dense fabric and layered with resin to create a shell that resists ballistic penetration. Kevlar has been the standard in military helmets for decades, valued for its proven performance against a broad range of ballistic threats and its versatility across different helmet designs. It’s heavier than the alternative but well-established and reliable.
UHMWPE is a newer competitor. Its molecular structure gives it outstanding tensile strength, and it’s one of the lightest materials used in ballistic helmets. For military personnel who wear helmets for hours at a time, that weight savings translates directly to reduced neck fatigue and better mobility. The tradeoff is that UHMWPE helmets can be bulkier at equivalent protection levels, and the material behaves differently across temperature extremes. Many modern combat helmets use a hybrid approach, combining aramid and UHMWPE layers to optimize both weight and stopping power.
How Safety Standards Shape Materials
The materials in your helmet aren’t chosen purely for performance. They also have to pass certification testing specific to the helmet’s intended use. Motorcycle helmets sold in Europe must meet ECE 22.06, which replaced the older 22.05 standard with more demanding requirements: higher impact speeds, testing across more zones of the helmet, and new tests for rotational acceleration. Bicycle helmets in the U.S. must meet CPSC standards, while industrial hard hats follow ANSI/ISEA requirements.
These standards set minimum thresholds for how much force can pass through to the head during a controlled impact. Manufacturers choose their shell and liner materials, along with their thicknesses and layering, to meet or exceed those thresholds while keeping weight and cost within range for their target buyer. A polycarbonate shell with EPS foam can pass the same certification as a carbon fiber shell, but the carbon fiber version will typically do it at lower weight, which is why you pay more for it.