Bike helmets in very cold weather
If you are going to be using a bike helmet in very cold weather you might wonder if the cold will affect helmet performance.
The CPSC and ASTM standard in the US do require that a helmet pass lab tests after conditioning in cold at temperatures in the range of -13 to -17 degrees C (F 9 to -1 degrees). Most other standards, including cold places like Canada, have a similar requirement. These temperatures should cover most bicycle riding. There are at least two other standards with lower temperature tests: the Swedish standard (now supplanted by the CEN European standard) had a requirement for testing at -20 C/ -4 F, the same temperature specified in both the current Snell Memorial Foundation B-90 standard and Snell B-95 standard. You can find lists of Snell-certified helmets on the Snell Web site. If you regularly ride at those lower temperatures it might be worth looking for a Snell-certified helmet. Here are the requirements of the various standards included in our Standards Comparison:
ASTM: -13 degrees to -17 degrees C (F 8 to -1 degree).
Australia/NZ -3 to -7 degrees C (F 41 degrees).
BSI: -8 to -12 degrees C (F 14 degrees).
Canada: -8 to -12 degrees C (F 14 degrees).
CPSC: -13 to -17 degrees C (F 9 to -1 degrees).
Europe: -18 to -22 degrees C (F -4 degrees)
Japan: -8 to -12 degrees C.
Snell B90: -18 to -22 degrees C
Snell B95: -18 to -22 degrees C
Snell N94: -18 to -22 degrees C
Sweden: -18 to -22 degrees C (minus 4 degrees F).
If for some reason you are using a bike helmet at lower temperatures, what should you expect? The EPS foam used in most bike helmets does stiffen somewhat at lower temperatures, but the impact performance has been tested at the temperatures listed above, so that is not serious. All of the plastic parts of a bike helmet could be expected to become more brittle while they are cold. This would include exterior shells, internal reinforcing and buckles. Buckles are reportedly tested at lower temperatures without any significant degradation. Internal reinforcing and exterior shells help to keep your helmet together for a second impact (typically when you hit the pavement after the first hit on the car) and their strength could be affected, although unless the helmet is stored outdoors it could take some time for cold to reach the internal elements. But once again, the buckle, shell and reinforcing have been tested at low temperatures to certify that they will meet the minimum requirements of the standard. And the conditioning before testing is long enough for the entire helmet to reach that lower temperature.
There is no permanent damage from exposing a helmet to cold weather--once the helmet warms up any effects of cold storage disappear.
Visors are worth a separate comment. Visors are not tested for shattering under the ASTM or CPSC protocols, or for that matter by other countries' standards. They might shatter in colder weather. In fact, they might shatter in cool or warm or hot weather too, and the helmet would still pass both of our US standards. That is part of the reason we don't advise using a visor unless you really need one for sun or rain problems. We have a page up with more on visors.
Cold weather comfort is easy to achieve with a bike helmet, even with temperatures well below freezing. An ear band is the place to start for most riders, since cold affects the ears unless they are held against the head and sheltered from the wind. A few helmets even come with detachable earmuffs. Those do not affect the helmet's fit, but a thin earband does not interefere either.
For more warmth, there are various ways to add a layer of cloth to your head under a helmet. Normally just a thin layer will keep your head quite warm, and that adds to the warmth of the rest of your body by limiting the heat loss from the head. Silk balaclavas cover everything including the lower face, and are so thin that they do not affect the fit of the helmet. You can also stuff vents with foam or put on a cover to eliminate airflow. But for some riders, moisture builds up under the helmet if all the vents are blocked.
Beyond your helmet, feet and hands are normally the limiting factor in how cold a ride you can stand. Keeping your body and head warm sends warmer blood to the extremities and helps keep feet and hands warm. Covering neck, wrists and ankles well prevents blood in major arteries from cooling in the airflow as you ride. Chemical handwarmer packets can make a big difference as well.
The best ski helmets are usually warm and meet an ASTM or Snell Memorial Foundation ski helmet standard that is very similar in impact protection to a bicycle helmet. That is not the case for CEN (European) standard helmets, since those are tested to a much weaker standard and should never be worn for bicycling. Be sure to check the sticker inside the ski helmet carefully for a statement that it meets ASTM F2040 or the Snell Foundation standard.
This page was last revised on: February 1, 2010.