Bicycle Helmet Safety Institute

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MIPS and Rotational Energy Management

Summary: The MIPS company holds a patent on one means of using a slip plane in a helmet. It may or may not help you avoid brain injury in a crash. Others have brought alternatives to the market. Studies testing with a biofidelic scalp on the headform have shown no benefit. Testing by two officers of the Snell Foundation showed no performance advantage. Lab tests demonstrated decades ago and more recently that you want the outside of your helmet to slide when you hit the pavement, not stick and jerk your head and neck. Rounder, slicker helmets are proven to do that better. We have only one report of scalp damage from a MIPS liner.

Study finds testing with scalp on headform shows no effect

A study published in Traffic Injury Prevention in 2020 showed that when researchers added a scalp to the test headform there was no effect from any of the three rotational mitigation technologies tested: "Results showed that when a biofidelic scalp layer is present, there is no statistical difference between helmet models with and without the anti-rotational technology in terms of rotational acceleration, velocity, relative rotation, impact duration and injury risk. " You can find the full study here.

Testing by two Snell officers shows no improvement

In 2018 the Snell Foundation's Bill Muzzy presented to ASTM's F08.53 subcommittee the results of testing by two Snell officers of MIPS performance using a linear impactor and offset (oblique) impacts. In the course of working on a test method for rotational injury they tested a MIPS and non-MIPS version of the same Specialized helmet. Their results with full details will be published in a journal soon.

Two of Snell's officers, working in a University of Washington test lab, dropped a 5kg guided impactor onto a helmeted Hybrid III headform and neck, impacting the helmet sides to achieve an oblique transmission of energy. The MIPS layer activated and moved. They used both flat and hemispheric impactors, and measured both linear and rotational acceleration. They hit each location twice. Helmet straps were tight. They chose the locations based on a Harborview study of the most likely impact locations on bicycle helmets.

The resultant data showed no significant improvement in the MIPS helmet's performance over the non-MIPS model. In some cases the non-MIPS model performed better.

The MIPS representative present at the ASTM meeting, Peter Halldin, said that he was not surprised, since MIPS' own testing with linear impactors had the same result. (MIPS normally tests with vertical drops on a slanted anvil. Most importantly, the headform is always free to move in any direction.)

See below for 2022 Snell testing of an unidentified rotational injury protection system.

Our conclusion is that this testing by officers of a respected organization with a distinguished history of consumer-oriented helmet activism, shows that MIPS is not likely to help you in a crash configuration similar to the one tested by the Snell officers. Other lab testing using an unrestrained moving headform with a sticky rubber covering and no neck attached impacting a very rough 45 degree slanted anvil with the straps tight over an inflexible jaw (the configuration MIPS uses) has shown that MIPS does reduce rotational acceleration. But when the head is constrained--as by a neck--MIPS does not perform well. That does not happen in the field, where heads are attached to the body. We still think your helmet, with a normal scalp under it, will move anyway.

In March of 2021 the Snell officers provided this clarification. We have revised the paragraph above to reflect the points they raised. See also the Snell 2022 publication below based on other test methods.

And here is the MIPS response from Peter Halldin

"You are welcome to send out my comments. For all of you I think that the understanding of the forces to the human head can be divided into the radial and the tangential force. In a bike accident as I see it there is a dominant tangential force. In the test presented by Snell there is a very small tangential force. This is also seen in the linear impact test machine designed by Biokinetics and used by NOCSAE. So, as I said in the meeting and that for some reason Randy misunderstood, I agreed in that the test showed by SNELL showed no reduction with MIPS. We have as I show in the attached PDF seen that the test method similar to the test by SNELL will not show a reduction for helmets like MIPS. We do have more than 17000 tests done in Sweden showing that all helmets with MIPS are significantly better than helmets without MIPS. We do have scientific evidence that a helmet with a low friction layer will make a difference in a test including a tangential force. So, as I told Bill Muzzy at the ASTM meeting I am willing to help out to design the test to mimic a realistic bike accident. With best regards, PETER"

In May of 2019 Consumer Reports published an article on their web page recommending rotational energy management as their first buying criterion for new helmet buyers, mentioning only MIPS and the WaveCel liners in Bontrager's helmets.

In May of 2019 the MIPS company purchased the brand Fluid Inside with its patents for another, completely different, type of rotational energy management.

Snell's 2022 test results

In 2022 the Snell Foundation reported on further testing of an unidentified rotational injury mitigation technology:

"The first of these series compared results for bicycle helmets equipped with one of the popular anti-rotational innovations with similar, almost identical helmets without this feature. We noted a 20% reduction in peak angular acceleration for frontal impact although the results for angular velocity were remarkably similar. However, the results for the third site halfway between a rear and a lateral impact showed almost no difference at all."


"This next series was also conducted on helmets with and without the anti-rotational feature. The test head forms were all treated with silicone but also with a wig firmly in place atop the head form over the silicone coating. When the results were compared, there appeared to be no real difference. The wig broke the coupling between the head form and the helmet so completely that the anti-rotational feature had no effect on rotational acceleration or angular velocity in this series."

and concluding:

We have demonstrated that at least one anti-rotational innovation can change the response of helmets tested in oblique impact. However, we have also demonstrated that different test protocols which might reasonably simulate field conditions may reduce the effectiveness of this innovation...Finally, although the testing has demonstrated that this anti-rotational feature does reduce peak angular velocity and peak angular acceleration for some tests conducted to FIM protocols, whether these findings bear on the protective performance of these features in real world crashes appears uncertain.

Background: MIPS and slip planes

A Swedish company called Multi-directional Impact Protection System - MIPS - has revived and patented the slip plane concept, using two layers in the helmet to help the head rotate slightly on impact. The hope is to reduce the rotational component of an impact, thought to be a prime brain injury mechanism and related to concussion.

From one Swedish manufacturer using their technology in 2009, MIPS developed marketing momentum after a 2013 article in Bicycling magazine praised it as the only new helmet technology available. We found six manufacturers in September 2013. In 2014 Bell bought a substantial part of the MIPS company, and other manufacturers began scrambling to put MIPS helmets on the US market. In mid-2016 there were 200 models from 58 brands. Does it work? Do you need it? We can not answer all of those questions below, but here is the story.

The first POC helmet with MIPS had two concentric layers, held in place by a pin that breaks and lets the shells slip for about 15 mm upon impact. The layer interface is coated with Teflon. Subsequent helmets we have seen have just a thin layer of uncoated polycarbonate plastic inside the normal helmet liner. It slips, but hold it down hard with your thumb and you can hear it creak against the EPS liner, indicating friction. MIPS says that the helmet is supposed to have a layer of slippery fabric between the foam and the polycarbonate insert, but that turns out to be just small fabric pads on some points. Not many models have a full layer of sliding enabler fabric, and we find many spots where the polycarbonate MIPS layer contacts bare EPS. In addition, the inserts are sliced up to avoid blocking vents in most helmets. The MIPS layer cuts down on ventilation where it impinges on vents. Bell has re-introduced the original POC concept with ball-and-socket models that have the MIPS layer between two liner layers.

Almost all of the early liners we saw left a large void in the back for the rear stabilizer, with a quarter or more of the helmet unlined and no slip plane effect if you hit at the rear. Although front and sides are more frequent impact sites, many impacts occur in the rear. We regard that as poor engineering, or hasty marketing at best. The Smith implementation has a grid of MIPS liner material, but with sharp Koroyd "straws" between that might dig into your skin and perhaps prevent the MIPS layer from working, depending on the crash angle and sequence. A few more recent liners have managed to cover the rear void.

We do not like the fact that the liner takes up space inside the helmet that could be devoted to a thicker crushable liner. MIPS says the liner is 0.5 to 0.8mm, reducing the helmet size by 1mm to 1.6mm, so the manufacturer would have to adjust the size in some way, either selling the consumer a larger helmet or reducing the thickness of the helmet liner. Slip planes do not repeal the laws of physics, and if you reduce the distance for stopping the head, it must be stopped more rapidly, increasing g's. So unless the helmet is made larger, we are skeptical that the thin inside MIPS layer will perform better than a thicker conventional helmet.

If it works, the effect of a slip plane is to reduce rotational energy momentarily for the critical first milliseconds of the impact sequence. The first two-layer POC helmet incorporating MIPS was very round and smooth on the surface as well, so they had minimal sliding resistance to begin with and the slip plane was available no matter where you hit. You can find more on POC in our Helmets for the current year page. In 2012 Lazer incorporated the first inner fit cage that was licensed by MIPS as well, on two of their child helmets. In short, the external configuration of a helmet is important in avoiding rotational force. Adding MIPS does not change that.

The helmet community has been discussing slip planes for years, and has been cautiously examining the MIPS data to evaluate the advantages if any. Everyone agrees that mitigating rotational force is important for injury protection, particularly for anti-concussion effects. But there are questions about how much a slip plane actually helps. Helmets are not coupled closely to the head, and will slip anyway. The scalp ensures that, and skin does not stick to EPS much, given sweat, hair, hair products and sunscreen. (The Koroyd "straws" pioneered by Smith Optics helmets might be a different story, given their known ability to abrade skin in a crash.) So the tendency for the helmet to slide on the user's head and to slide on pavement or other impact surfaces is substantial. The Snell testing reported on above seems to confirm that.

MEA Forensic has published a paper on their research showing that when a helmet slips on the head it reduces peak acceleration and peak angular acceleration. You can access the abstract on the ResearchGate site. The article is titled The effect of hair and football helmet fit on headform kinematics. It is very likely that football helmets are more closely coupled to the head than a bicycle helmet due to their construction and additional coverage.

Triathlete magazine published an article in 2023 about MIPS based on a second MEA study that tested bicycle helmets. The Triathlete author missed the point of the study entirely, since the research showed that MIPS would reduce rotational force, but then tested with a stocking or a wig on the sticky urethane-covered headform and found that they provided approximately the same reduction. Your head is not sticky urethane, so the stocking and wig provided more realistic conditions and raised serious questions about how much MIPS helps on a real head. The Triathlete headline asks "is MIPS worth it" but the real question is does MIPS really work.

An article in the May/June 2016 issue of Consumers Digest available only behind their pay wall reported that their interviewees did not offer strong support for MIPS. A Snell Memorial Foundation employee was quoted at that time as saying that in her opinion MIPS is "snake oil to get people to spend money."

There is even the question of how much you would want your helmet to slip. This study calculates risk factors for helmets that slip due to poor fit, and how much that increases the risk of head and facial injury. A MIPS helmet has a very small amount of slippage designed in.

A slip plane might help if the impact surface did not permit sliding and the head is rigidly coupled with the helmet. MIPS uses computer brain simulations to support their claim that it performs in a lab test when the helmet is tightly strapped on the headform, particularly if the surface of the headform is relatively grippy rubber. Other labs have not found similar effects. We are more cautious than the patent-holder, and are still looking for test data from other sources and for any field experience that would show that the technology will actually reduce injuries, and in what situations.

Whatever the performance verdict for MIPS, their marketing took off after the Bicycling article. Bell then purchased a substantial stake in the MIPS company, so they were committed to it and wanted direct access to the MIPS expertise. They are still marketing some of the worst examples of missing rear MIPS liners. Other manufacturers are giving in to the marketing and fashion push. A Bell restructuring actually placed the MIPS holdings in a different company, but their direction was set.

MIPS announced at Eurobike in August 2017 two new versions of their product. Both are variations of the basic slip plane, with the slippery plates encased in stretch fabric. One is a cap covering the whole head, suitable for unvented helmets. The other consists of fabric circles with slippery material in the center, to be placed between vents in a helmet with that much liner space between vents. MIPS is obviously trying to keep up with the alternatives below.

Injury reports

Possible scalp damage

We have only one report of a damaged scalp apparently from a MIPS liner. Here is the photo the rider sent us. Scalp damage apparently from helmet liner
The rider is alive and well, and did not report any brain damage, the most significant result.

Hair loss

We have one very credible report of a child with long hair whose hair gets caught in the MIPS add-on in his helmet, resulting in hair loss every time he removes it.

There are millions of MIPS helmets in use, but we have just those two reports.

MIPS has reported that their technology is now in 883 helmet models from 143 brands, for a total of 12.6 million helmets in 2021. In 2023 MIPS purchased 25% of Quin, a motorcycle helmet manufacturer known for embedded sensors and automotic crash detection.

Alternatives: Trek, 6D, Leatt, Kali, POC, HEXR, many more

As concussion awareness has risen, many manufacturers are working on alternative solutions to address the rotation question. Helmet companies say "you have to have a story on concussion protection." One company has a European grant to develop a technology that changes the structure of an EPS liner to permit movement on impact. 6D has demonstrated that its technology performs well in lab testing. Leatt and Kali also have helmets with liner "doughnuts" that may permit head motion on impact. And POC, the original MIPS user, introduced a similar alternative in 2018 that it calls SPIN pads, placed around the interior of the helmet to promote lateral movement of the helmet in a crash. (A MIPS patent-infringement lawsuit against POC has now been settled.) Trek has introduced their WaveCel liner, with a mesh that can collapse at an angle to attempt to reduce rotational force. HEXR says their honeycomb liner reduces rotational force as well. Although unbiased test results are very hard to find, any spur to innovation after what has been a long, stagnant period for new helmet technology is very welcome. See our page on Rotational Injury for more on other systems, and other elements of the rotation problem including the sliding resistance of the shell.

Our bottom line

Do you need MIPS? Using careful evaluation, and in light of the Snell testing showing no benefit in their test configuration or with an unidentified technology and a wig, we are still not convinced that you do. It may help in some impacts and probably won't hurt, other than any effect on ventilation, of if your manufacturer has kept the same outer profile and reduced the thickness of the inside energy management liner to accommodate the MIPS layer, or if it lets the helmet slip too much, or if it pulls your hair out, or if the extra cost of the MIPS model makes a difference to you. We do not see compelling evidence that you should trade in your current helmet on a MIPS model unless having the Latest Thing is important to you. Based on Snell's research we think the jury is still out on MIPS. There are alternative rotational energy management systems in the market. We think your first concern should be to wear a helmet with a round, smooth exterior that will not snag as you slide on the pavement.