Collapsible Bicycle Helmets Protect Less on Average, Imperial Tests Find

If you line up 30 bicycle helmets on a lab bench, they all seem similar: foam shells, air vents, chin straps. But when you test them the way a cyclist’s head actually hits the road - at an angle - the differences become clear. Engineers at Imperial College London did just that and discovered that collapsible bicycle helmets, which fold flat to fit in a bag, generally offer less protection than regular helmets.

Researchers from the HEAD Lab at Imperial’s Dyson School of Design Engineering tested 30 helmets sold in stores - 24 regular models and all six collapsible models available in the UK.^[1] All the helmets met the minimum safety standards required by regulations.^[2] The difference only showed up in a test that these standards don’t include.

Current certification tests drop helmets straight down and mostly measure the direct force of the impact.^[3] However, most cycling crashes happen at an angle, causing the head to rotate quickly.^[4] To reflect this, the Imperial team hit each helmet at four different spots, repeated each test three times with a new helmet, and used a tall drop rig to measure both straight and rotational head movements.^[5][6]

What the tests found on collapsible bicycle helmets

On average, the predicted risk of a straight-impact injury was 24% for collapsible helmets and 20% for regular ones.^[7][8] For brain injuries caused by head rotation, the team found no difference between the two types.^[9] Still, five out of six collapsible helmets ended up in the lower half of the protection rankings.

Weight plays a major role here. Collapsible helmets were about 57% heavier than regular ones, averaging 461 grams compared to 294 grams.^[10][11] The researchers estimate that every extra 10 grams adds about 0.2% more risk. Paying more doesn’t mean better safety either: the collapsible helmets in the study cost £101 on average, while regular ones cost £64.^[12]

There is good news for designers: the gap isn’t an unavoidable part of folding helmets. One example proves this. The Newlane Foldable with MIPS, a system for rotational protection, ranked second out of all 30 helmets, while the version without MIPS came in 26th.^[13] Only one of the six collapsible helmets had rotational protection, compared to 12 out of 24 regular helmets.^[14]

Lead author Dr William Dawber understands why folding designs are popular: “Collapsible helmets are a great solution to overcome inconvenience.”^[15] Professor Mazdak Ghajari, Professor of Brain Biomechanics and founder of the HEAD Lab, also emphasizes that people should keep using them: “Any helmet is safer than no helmet and innovative designs that appeal to more people are to be applauded.”^[16]

Biomechanics is the field that turns crash forces into injury risk, and it’s one of the areas covered in our guide to biomedical engineering careers. You can find the full results in Imperial’s announcement and in BikeRadar’s report.

What happens next

The researchers believe that adding rotational protection and reducing weight could close the safety gap, and they share their results so manufacturers can make better helmets. The challenge now is to design a helmet that folds up small, stays light, and still gives the foam enough space to crush. That’s a design problem any engineering student could start working on today.

What this means for you

This study involved design engineers who create helmet shells and foams, biomechanics researchers who translate crash forces into injury risk, and test engineers who operate drop rigs and analyze sensor data. These careers usually begin with a degree in design, mechanical, or biomedical engineering, and our guide to mechanical engineering careers explains the different paths, including vocational options. Physics connects everything, and our guide to A-level Physics for engineering shows how learning about forces and motion can lead to a career.

Image: Imperial College London