Bike helmets in very cold weather
Summary: If you are going to be using a bike helmet in very cold weather you might wonder if the cold will affect
helmet performance. Helmets are tested for that.
The CPSC and ASTM standard in the US 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 website
. 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
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
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 interfere 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.