Bicycle Helmets and Do-Rags
Summary: Caps or do-rags worn under helmets can affect fit, but are ok to use as long as the helmet fits well with the cap in place.
Various manufacturers are selling do-rags (a cloth that goes on the head) to fit under helmets for either sun protection in the summer or heat retention in winter.
Putting a thin cloth beneath your helmet raises some questions. Is fit affected? Is your head now more slippery, letting the helmet slide around in a crash or even flip off?
Bald riders will realize that a cotton cloth or sunscreen cover on your head is not as slippery as skin with sweat and suntan oil on it. In addition, those who use a cover on their heads in summer to avoid funny tan lines usually fold the cloth so that it does not continue down the sides, where it would come between the fitting foam and the head. (We have more on our bald rider page.)
What about those with hair? We are not sure. The cloth could possibly make your head more slippery than hair, even hair with sweat and oil on it. But the real work of keeping the helmet on your head is done by the straps, not the friction between fitting foam and the head. We believe that if the straps are not adjusted correctly, the helmet will be less likely to stay on, no matter what the surface of the head is like.
If you think about how head covers might influence the grip between helmet and head, it would seem that some of what a do-rag does is to increase the size of the head a little bit, squishing the fitting foam just a little more and raising the helmet just a bit, putting a tiny bit more pressure on the chin strap. That is assuming people don't readjust anything unless the head covering is really thick. Balance that against whatever effect the do-rag may have on the friction between helmet and head, and the effect is likely to be small. Although we have no good way of testing this hypothesis scientifically, that would seem to indicate that do-rags will probably not make the helmet more likely to come off in a crash. Some have tried it with the rolloff test in the ASTM and CPSC standards, and have found no effect. But that test is too crude to provide a good indicator.
If you use a do-rag in summer or a winter cap under your helmet, you can help. Put your helmet on with and without the cloth, and try to tear it off. Let us know with an email if you detect a real difference.
Our best guess is that do-rags are probably ok for most riders if the helmet is properly adjusted with the cap or cover in place and passes the tests for a well fitted helmet.
This page was revised on: October 27, 2020.