Collapsible bicycle helmets are convenient and portable, especially for people jumping on a hire bike. But new research from the HEAD Lab at Imperial College London suggests they might not be the safest choice.The study was funded by The Road Safety Trust and is said to be the first to compare protection provided by collapsible (or foldable) foam helmets and conventional helmets.It tested 30 commercially available helmets, including six collapsible models, across four impact locations, using a tall drop rig to measure linear and rotational head motion.The researchers found that collapsible bicycle helmets provide lower levels of protection against serious head injuries than non-collapsible helmets.This research will feed into the HEAD (Human Experience, Analysis and Design) Labs Helmet Impact Protection Effectiveness Rating (HIPER) system.Similar to Virginia Safety Tech, this provides consumers with safety data on different helmets and provides manufacturers with insights.Mazdak Ghajari, professor of brain biomechanics at the Dyson School of Design Engineering and a founder of the HEAD Lab, said any helmet is safer than no helmet and that innovative designs that appeal to more people should be applauded. You may like: Are bike helmets about to get safer? This test lab is on a mission to make that happen4 percentage points The MET Vinci MIPS was the top-rated helmet in the study. Ashley Quinlan / Our Media The study found that collapsible helmets presented a higher risk of linear injuries, which include skill fractures and focal brain injuries.The average predicted risk of a linear injury was 24% for collapsible helmets compared to 20% for conventional helmets.While the difference in linear injury risk may seem relatively small, researchers note that even a 4 percentage-point increase could translate into a substantial number of additional serious head injuries overall, a press release for the study reads.However, the study found no difference in protection against brain injuries caused by rotation of the head, which additive technologies such as MIPS are designed to protect against.The researchers said the greater weight of collapsible helmets and the limited use of technologies to protect against rotational impacts contributed to their lower average safety performance.Collapsible helmets were on average 57% heavier than conventional helmets (461g versus 294g). Increased helmet mass was associated with greater linear injury risk, with an average increase of 0.2% risk per additional 10g on a helmet.In addition, rotational protection technologies reduced both linear and rotational injury risks but were used in only 1 of 6 collapsible helmets, compared with 12 of the 24 conventional helmets, according to the press release.Room for improvement The presence of MIPS was found to be a key factor in helmet safety ratings. Sam Voaden / Our Media Overall, five of the six collapsible helmets tested during the study ranked in the bottom half of the protection rankings. But the researchers found the performance gap was not inherent to the helmet designs.This was illustrated by testing two versions of the Newlane Foldable helmet. One incorporated MIPS, while the other didnt have the technology.The MIPS helmet ranked second among the 30 helmets, matching or superseding most of the conventional helmets. It achieved a score of 82.3 out of 100 and a platinum rating, which is HIPERs second highest rating.HIPER moved from a star ranking to a ratings model in 2026 and no helmet has achieved the top ranking of diamond, which requires a score of more than 85.Meanwhile, the Newlane Foldable helmet without MIPS achieved a score of 71.9 and silver rating.So, despite their lower performance, the researchers found these collapsible helmets can be an excellent solution to make helmet use more accessible for cyclists. Which were the safest helmets on test?Out of the 30 collapsible and conventional helmets on test, the MET Vinci MIPS ranked highest, with a score of 83 and a platinum rating.The Newlane Foldable helmet with MIPS came second and the MET E-Mob MIPS came third with a score of 80.3 and a platinum rating.You can see the full results on the HIPER website.