Bike Helmet Technology Explained

Helmet spec sheets are full of acronyms. MIPS, EPS, EPP, in-mould, polycarbonate, aramid. Most of them describe real differences in how a helmet is built and how it behaves in a crash, but almost nobody explains what they mean in plain terms.

This page does that. If you want help choosing which helmet suits your riding, start with our bike helmet range, which covers helmet types and sizing. This page is for understanding what you are looking at once you are comparing two helmets on paper.

Liner Materials: EPS and EPP

The liner is the thick foam inside the helmet. It does the actual work of absorbing an impact. The shell holds it together and spreads the load, but the liner is what protects your head.

EPS (expanded polystyrene) is what most bike helmets use. It absorbs impact energy by crushing. That crushing is permanent, which is why an EPS helmet is a single-impact product: once the foam has compressed, that area of the helmet cannot do it again. This is the reason every helmet manufacturer tells you to replace a helmet after a crash, even when it looks undamaged from the outside. The damage is inside the foam and you usually cannot see it.

EPP (expanded polypropylene) recovers its shape after an impact, which makes it multi-impact capable. It is heavier and bulkier than EPS for the same protection, and more expensive, so it is uncommon as a full liner on a bike helmet. Where you will see it is in hybrid designs, where a manufacturer uses EPP in specific areas and EPS elsewhere to get the strengths of both.

The practical takeaway: assume your helmet is single-impact unless the manufacturer explicitly says otherwise.

Shell Materials

The outer shell protects the liner from everyday knocks and spreads impact force over a wider area of foam.

In our range, the Seven iDP Project 23 is sold in both a fibreglass and a carbon version, which is a clear example of the same helmet design at two weights and two price points. At the other end, the Kask Valegro uses an in-mould polycarbonate shell to get its weight down without carbon anywhere near it, which shows that shell material alone does not determine how light a helmet ends up.

In-Mould and Hard Shell Construction

These are the two ways a shell and liner get joined together, and the difference affects weight, ventilation, durability and price.

In-mould bonds the shell to the foam liner during manufacturing, in a single piece. The shell can be very thin because it is supported by the foam across its whole surface. Result: lighter, better ventilated, cleaner looking, and the helmet deforms more readily during an impact, which is what you want. Almost every modern road and open-face MTB helmet is in-mould.

Hard shell moulds the shell and the liner separately, then joins them. The shell is thicker and tougher, which handles scrapes, drops and being thrown in a bag far better. It is heavier and has less ventilation. This is why skate-style, BMX and many children's helmets use it: those helmets get knocked about off the bike more than on it.

Both are safe. Both are certified to the same standards. The choice is about weight and ventilation against durability and price, not about one being more protective than the other.

Rotational Impact Systems

This is the biggest change in helmet design of the last fifteen years, and MIPS is only one version of it.

The problem they all address is the same. Helmet certification tests drop a helmet straight down onto an anvil, but real crashes are almost never a direct vertical impact. You hit the ground at an angle, your head rotates suddenly, and that rotational acceleration is the mechanism associated with concussion and more serious brain injury. A liner that handles linear impact well may do nothing about rotation.

The responses fall into three groups, and only the first two are things built into the helmet.

Slip-plane systems let the shell rotate slightly relative to your head, absorbing some rotational energy before it reaches you.

• MIPS (Multi-directional Impact Protection System) is the most common. A low-friction layer inside the helmet allows roughly 10 to 15mm of movement in any direction. Developed in Sweden with input from a neurosurgeon and a biomechanics researcher. Identified by a yellow MIPS logo, usually on the back of the helmet. MIPS is a licensed technology, which is why you see it across many brands rather than just one.

Structural systems build the rotational management into the liner itself rather than adding a layer.

• Lazer KinetiCore uses engineered crumple zones moulded into the EPS liner itself. Because nothing is added on top of the foam, these helmets can come in lighter and better ventilated than a MIPS equivalent at the same price, and there is one less component to wear out. We stock it across the range, from the Lazer Maze for everyday riding through to the Strada for road.
• Other brands run their own versions. Our Seven iDP Project 23 full face helmets are listed as S.E.R.T. equipped, which is Seven iDP's own system.

Test protocols are a third thing, and they are frequently confused with the first two.

WG11 is the one you will see most often, usually on Kask helmets. It is not a technology and there is no WG11 component inside the helmet. WG11 is a European working group of industry experts, independent test laboratories, manufacturers and academic researchers, formed to standardise how rotational and tangential impacts are tested in the first place. The problem it addresses is upstream of any helmet: certification standards test straight-line impacts, so until there is an agreed method for testing angled ones, manufacturers have no common way to prove a rotational claim.

Kask tests its helmets to the WG11 protocol at Newton Lab, an independent certified facility in Milan. Every Kask helmet we stock carries it, which is why WG11 appears in the model names themselves: the Mojito 3, Mojito Cubed, Protone Icon, Sintesi and Valegro.

The distinction is worth understanding because retailers routinely list WG11 in a features row next to MIPS as though you are choosing between them. You are not. MIPS and KinetiCore are things a helmet has. WG11 is a test a helmet has passed. A helmet could in principle have both.

Is it worth the extra money? If you are choosing between two helmets you otherwise like equally, take the one with a rotational system. If it means stepping down to a helmet that fits you worse, do not. Fit does more for your safety than any technology inside the helmet, because a helmet that moves out of position during a crash cannot protect the part of your head that hits the ground.

Australian Helmet Standards

The rules changed in 2024 and most retailers have not updated their information.

Under the Consumer Goods (Bicycle Helmets) Safety Standard 2024, six standards are accepted for bicycle helmets supplied in Australia:

Before this, AS/NZS 2063 was effectively the only accepted route. It is still the most common certification you will see on helmets sold here, particularly road, recreational and kids helmets. But full face mountain bike and BMX helmets are frequently certified to CPSC or ASTM instead, and that is entirely legal.

Every helmet in our range is certified to at least one of the six. The certification label is inside the shell, usually on the liner or under a pad, and shows the standard it was tested to. AS/NZS helmets also carry a five-tick StandardsMark or an equivalent certification mark.

Worth knowing if you buy from overseas websites: a helmet that meets none of these six is not legal to use on Australian roads, regardless of how reputable the brand is. Check before you buy, not after it arrives.

Visors

A visor shields your eyes from low sun, rain, mud and whatever the wheel in front of you throws up.

Road helmets almost never have one. On a road bike you are leaned forward with your head down, and a fixed visor sits directly in your sightline when you look up the road. Road riders use a cycling cap with a soft peak or just sunglasses instead.

MTB and recreational helmets usually do have one, because you sit more upright and you are far more likely to meet mud, branches and spray. Better MTB helmets use an adjustable visor that flips up out of the way, which matters when you are running goggles or riding a steep descent with your head down. The Giant Path MIPS in our range has a removable visor, which is the simplest version of the same idea.

There is no safety difference. It is a comfort and visibility choice.

Retention Systems and Buckles

Dial systems tighten a cradle around the back of your head. Almost universal now. The thing to test in a shop is not how tight it goes but how well it holds the fit while you move, and whether it adjusts for height as well as circumference. A cradle that sits too high leaves the back of your head loose.

Magnetic buckles are the one feature most people notice immediately. The Fidlock SNAP buckle closes with one hand, in gloves, without looking. Once you have used one, a standard side-squeeze buckle feels like hard work. Our Fox Dropframe Pro Flow uses one.

BOA dial fit is borrowed from cycling shoes and gives finer adjustment than a standard ratchet dial. The Fox Dropframe Pro Flow uses this as well.

Strap dividers are the unglamorous part that matters most. The Y-junction where the straps meet should sit just below your ear, and it should stay there. Cheap dividers slip and the helmet ends up sitting back on your head, which is where most badly fitted helmets go wrong.

Light and Camera Mounts

Some helmets are designed to take a rear light clip or a camera mount rather than needing an aftermarket strap-on.

For commuting, a rear light at helmet height is seen by drivers earlier than one on the seatpost, because it is closer to their eye line and less likely to be blocked by panniers or your own body. It does not need to be an integrated one. A clip-on rear light on the back of any helmet does the same job.

Camera mounts are mostly a full face and trail helmet feature. If you plan to run a camera, check how it attaches: an adhesive mount on a thin in-mould shell is not ideal, and a breakaway mount is the safer design in a crash.

Full Face, Open Face and Convertible

Open face is the standard helmet shape with no chin bar. It covers everything except your jaw and face. Suitable for road, gravel, commuting, cross-country and most trail riding.

Full face adds a fixed chin bar. Required for downhill, bike park and sanctioned BMX racing, and increasingly common for enduro. Modern full face helmets split into two quite different types: heavy, maximum-protection gravity helmets, and much lighter, heavily ventilated ones you can actually pedal uphill in.

Convertible helmets have a removable chin bar so one helmet covers both. The Kali Maya in our youth range works this way. Good compromise for a rider who does one uplift day a year, less good if you do it every weekend, since a dedicated full face is stronger and a dedicated open face is lighter.

For sanctioned BMX racing, AusCycling requires a full face helmet with a fixed, non-detachable mouthpiece. A convertible helmet does not satisfy that rule.

Glossary

ABS (acrylonitrile butadiene styrene). A tough, hard thermoplastic used for hard shell helmet shells. Heavier than polycarbonate, better at resisting scrapes and knocks.

Aramid. A high-strength synthetic fibre, sold under the trade name Kevlar among others. Used to reinforce thin in-mould shells against penetration.

AS/NZS 2063. The joint Australian and New Zealand bicycle helmet standard. Exists in a 2008 and a 2020 version, both currently accepted.

BOA. A dial-based fit system using a steel lace, borrowed from cycling shoes, offering finer adjustment than a standard ratchet.

Carbon fibre. Very light, very strong shell material. Found on premium full face helmets where weight is the priority.

EPP (expanded polypropylene). A liner foam that recovers after impact, making it multi-impact capable. Heavier, bulkier and dearer than EPS.

EPS (expanded polystyrene). The standard liner foam. Absorbs impact by crushing permanently. Single impact only.

Fidlock. A magnetic buckle system that closes and releases one-handed.

Hard shell. Construction where the shell and liner are made separately and joined. Tougher and heavier. Common on BMX, skate and kids helmets.

In-mould. Construction where the shell is bonded to the liner during manufacture. Lighter and better ventilated. Standard on road and open-face MTB helmets.

KinetiCore. Lazer's rotational impact system, built into the EPS liner as crumple zones rather than added as a separate layer.

MIPS (Multi-directional Impact Protection System). A low-friction layer inside the helmet allowing roughly 10 to 15mm of movement to reduce rotational force. Marked with a yellow logo.

Polycarbonate. A light, strong shell plastic. The most common in-mould shell material.

Rotational impact. Force applied at an angle that causes the head to rotate suddenly. Associated with concussion and more serious brain injury, and the problem that systems like MIPS are designed to address.

StandardsMark. The five-tick certification mark found on AS/NZS certified helmets.

WG11. A European working group standardising how rotational and tangential impacts are tested. Not a helmet technology. A helmet described as WG11 has been tested to that protocol, most commonly by Kask, which tests at Newton Lab in Milan.

Ready to shop?

Browse our full bike helmet range, or go straight to road bike helmets, MTB helmets, full face MTB helmets or kids bike helmets.

Helmet fit varies more between brands than the size labels suggest, because manufacturers build on different head shapes. Two helmets both marked medium can feel completely different, and no amount of reading gets around that. Every helmet we sell is fitted and sized properly at the counter before you leave, for kids and adults alike. It is the one part of buying a helmet that a website cannot do for you. Ivanhoe Cycles has been fitting riders since 1986.