Impact liner
VisibleExpanded polystyrene (EPS), typically 60–90 g/L
EPS crushes at a near-constant force over its thickness, which is what limits peak deceleration. It does not spring back — once crushed, that area is spent.
What is a bicycle helmet made of?
A helmet works by being destroyed. Its main material is a foam engineered to crush at a controlled rate, converting the energy of an impact into permanent deformation instead of passing it to your skull.
What a bicycle helmet is made of, part by part
7 parts — 6 you can see, 1 you can’t without opening it.
Outer shell
VisiblePolycarbonate, in-moulded onto the EPS
It spreads point loads across the foam and lets the helmet slide rather than catch on impact. In-moulding bonds it during expansion instead of gluing it on.
Internal reinforcement
HiddenNylon or polycarbonate skeleton, sometimes aramid strips
It holds the EPS together after it has cracked so the helmet stays on your head through a multi-impact crash.
Rotational-impact layer
VisibleLow-friction polymer slip-plane, or an elastomeric suspension
It allows a few millimetres of movement between head and shell, reducing rotational acceleration — the mechanism most associated with brain injury.
Straps
VisibleWoven nylon or polypropylene webbing
Webbing has almost no stretch under load, so the helmet stays positioned. Nylon resists UV and sweat degradation better than polypropylene.
Retention cradle
VisibleGlass-filled nylon with a ratchet adjuster
Fit is what makes the rest work. A helmet that shifts before impact is not in the right place at impact.
Padding
VisibleOpen-cell polyurethane foam with a polyester cover
Comfort and fit only — it contributes essentially nothing to impact protection, despite being the part you feel.
What the materials list doesn’t tell you
The comfort padding you notice does no protective work, and the EPS that does all of it is single-use. A helmet that has taken a real impact can look completely intact while the foam under the shell is fully crushed.
Can it be repaired?
Not repairable, by design. Straps and pads are replaceable; the EPS liner is not, and a helmet that has been crashed should be replaced even with no visible damage.
Common questions
- Do I need to replace my bike helmet after a crash?
- Do bike helmets expire if you never crash them?
- Are expensive bike helmets safer?
Yours won’t be exactly this one
This page describes the category. Exploded reads the specific object in front of you — photograph your bicycle helmet and get a breakdown of its parts, with every guess labelled as a guess, then explore what could be built differently.
Analyze your bicycle helmet