Bicycle Helmet Safety Institute

An anti-concussion helmet?

Summary: Some years back we asked two noted helmet experts what thickness of foam would be required to turn a current bike helmet into an anti-concussion helmet by keeping the CPSC two-meter flat anvil drop test below 100g. Here is the result.

What's new in concussion?

If you are looking for significant trends in the concussion dialogue, you can start with the realization that impacts cause injury, even if the injury is minor and not diagnosed. There is no "threshold of concussion." Mild traumatic brain injury is difficult to explain or predict from a given impact location, direction and severity. Rotational injuries occur from straight-on impacts. The brain models and impact sensors don't do a good job of predicting real-world injury. So even though most bicycle riders suffer fewer impacts than football players, they should probably still be concerned with helmet performance in lesser impact scenarios. BMX or downhill mountain bike racing competitors who fall often should certainly be concerned. But no bike helmet standard is currently testing for low-velocity impact performance or for rotational force. Stay tuned.

Anti-concussion helmet?

Today's concerns about concussions have raised the question "who has an anti-concussion helmet?" We have a difficult time answering that one.

In response to a recent ASTM ballot challenge, two notable helmet experts prepared an analysis for us explaining what thickness a helmet would have to be if made with today's standard EPS foam to keep the g's below 100 in the drops included in the CPSC standard. At the time, we thought you might still be concussed at 100g but the odds are with you that it will be mild. More recent research is showing that the concept of a threshold of concussion is probably obsolete, but we needed to pick a benchmark somewhere.

Dr. Terry Smith, then Senior Scientist at Dynamic Research, and Daniel Pomerening then of SouthWest Research Institute collaborated on this paper explaining the complexities of foam thickness to achieve that.
We mocked up a helmet with their parameters, and it came out looking like this: Obviously this design is much too large to be practical. The circumference is bumped up to 45cm. (Perhaps more if we added MIPS.) The weight is a problem, in particular because the bulk of it is above the head's center of gravity where weight is most bothersome. Vents would not work well, if there were any. But most importantly, in a crash the leverage this helmet would exert on your head and neck would be increased dramatically by that thicker foam, upping the dreaded rotational energy to the head and perhaps making it not an anti-concussion helmet at all.

There are other materials, of course, but no published test results indicating that there would be a major difference. The good news is that the Smith and Pomerening analysis postulates that with a perfectly efficient material in place of EPS foam the liner could be much, much thinner. We call that material unobtainium and look forward to seeing it on the market some day.

Anti-concussion helmet add-ons?

A 2015 study of football helmet add-ons, including soft outer shells, spray treatments, pads and fiber sheets found that "there is no magic concussion prevention product on the market at this time." More recently in 2022 some NFL teams have been experimenting with an add-on for their football helmets that puts a pillow-like layer on top. We don't know if the results have been published yet. In 2024 players have begun using the add-ons in actual games, and saying they like the additional padding.

Another study was conducted at Stanford University and published in 2022 titled Padded Helmet Shell Covers in American Football: A Comprehensive Laboratory Evaluation with Preliminary On-Field Findings. The researchers found that an exterior football helmet add-on seemed to enhance protection in lab tests, but when tested in the field showed no improvement in protection for actual athletes wearing the helmets. "However, on the field, no significant differences in any measure of head impact magnitude were observed between the bare helmet impacts and padded helmet impacts."