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Try searching for the term "ear band". They tend to be thin enough to comfortably wear under a helmet, and the good ones are fully wind-resistant, yet breathable.

If you have an open ventilation-style helmet, I recommend a helmet cover as well, which is a fabric sleeve that stretches over the top of the helmet which also significantly cuts wind passing through, and may be easier to use instead of a jacket hood (not to mention more streamlined). Install once per season.

Balaklavas or "dickies" are also good to protect the neck and shoulders, and there are also polar fleece neck warmers that may be more comfortable and can bunch up nicely under the back of the helmet.

Any quality of biking glasses/goggles are useful, too — look for ones with clear lenses — which will ensure your eyes don't get a full blast of cold directly.

I have a thin material tube that can be used for a lot of things. Also called a headsock or necksock or a buff.

I wear mine around my neck, with the top edge at my mouth/nose, and up over my ears at the back. The lower edge rides on my shoulders and slightly over my collarbone. Some buffs have a split on both sides and cover the top of the chest a bit.

Then on top of this I wear a cycling cap with a visor (my commute is into the sun both ways and helmet lacks a visor.)

Downsides, covering the mouth leads to problems with dampness from the breath, and contributes to steamy glasses.

Also, if you're biking fast enough you warm up with the effort and can get too hot, even in the cold.

Links:

• https://www.dx.com/p/all-seasons-multi-functional-headwear-grey-124608#.W-k-P3UzbmE


• https://www.dx.com/p/all-seasons-multi-functional-headwear-violet-274338#.W-k-H3UzbmE

This is an unconventional answer but it works for me.

I have an aero TT helmet that has fairings over the ears. The reason the fairings exist is to reduce my head's aerodynamic drag, but in doing so, it also takes my ears out of the boundary layer and keeps them toasty warm in winter.

Good luck

Living in Sweden, I know what you're talking about. Because I like wearing a hat for any temperature below 10°C (50°F) and it can be -20°C (-4°F) in the winter, I have a special hat for usage under my bicycle helmet. For the warmer days I just use a thin buff, which I can always keep in my pocket due to its limited size. For the colder days I have a hat without anything on top of it (e.g. no pom-pom). I noticed the helmet is not very friendly for the fabric, it will wear out a little bit and start looking ugly, so do not use your favourite hat for it. Because the thickness of the hat is just a few millimetres, only a small adjustment of the helmet is needed.

When it's cold enough here, I use a toque (or beanie or knit cap or whatever you call it in your part of the world) under my helmet. It's thin enough that a small adjustment of my helmet is all that is needed for a comfortable fit. Mine fits over my ears and doesn't interfere with headphones.

I have a chillcheater skull cap for kayaking. It's designed to fit under a helmet and keeps the wind off your ears while also holding them closer to your head (warmer in its own right). I've tried it on the bike in a UK winter, and found it too warm for significant effort -- but our winters are warmer.

Having a proper headwear under your helmet should be a preferred way to keep oneself warm. However, for the picture's completeness, I want to mention using different types of helmets in winter: full-face MTB and moped/motorcycle helmets.

They are heavier and pricier than regular "open" helmets, but they have much less ventilation, and often come with some sort of goggles to cover your face even more. Both aspects are beneficial in winter.

Another thing is that these helmets are also certified for riding two-wheeled (non-)motorized vehicles, if this is something you are concerned with. Other types of "warmer" helmets, such as ski helmets or water-rafting helmets, may not be tested against the types of impacts that may happen in a bicycle/motorcycle crash. You need to check certifications of a helmet before using it in possibly unintended conditions.

There are literally hundreds of cycling specific headwear items available in the US that can keep your head and ears warm in cold weather, that are thin enough to fit under a helmet (and not look too strange).

Just google 'bicycle headwear cold' and you'll find many choices; from headbands that keep the ears warm, but allow for cooling from the top of the head; simple skullcap type hats that insulate head and tops of ears; hats with extended ear and neck protection flaps; to full-face and neck balaclavas.

I've even seen casual cycling helmets that come with a fitter liner with ear flaps that attaches to the chin strap 'fork' that goes either side of the ears.

We've got plenty of good answers already so just want to share my head warm set up depending on the temperature. I also live in Sweden and in my daily commutes experience from +25C to -20C.

+15C and up - only helmet, no head wear.

+5C to +15C - helmet with a cycling cap.

+0C to +5C - this is where stuff gets serious. On the upper limit of the range it could still be acceptable to ride without any ear protection in a normal cycling cap, due to the fact that our ears (or at least mine) adapt really quickly to cold by increasing a blood flow. Otherwise light ski scarf on the ears could help, or light cycling cap with ear cover.

-10C to +0C - for these conditions it's impossible to live without ear covers. I have winter cap with ear covers which is too warm, so mostly I use thin balaclava which goes around my face. Winter cap is not perfect for such conditions because you would also want to cover your neck. So too warm winter cap with ear covers in my case feels like a bad purchase.

-20C to -10C - in these conditions it's very important to both protect your face and your lungs. This is when I go for a full face balaclava for cycling with breath holes and ski goggles.

Hope my experience would help anyone to stay warm :)

UPD: also would like to add that commuting in cold temperatures adds unexpected requirements to your face wear. When it comes to lower than 0+ temperatures I also use protective lipstick (very greasy, you come to this naturally) and of course always use protective glasses, transparent for the dark part of the year, which are getting replaced by ski goggles when stuff gets even more serious.

My wife knitted me a pair of bike helmet earmuffs from a pattern similar to this: http://brineydeepdesigns.blogspot.com/2008/10/free-pattern-bike-helmet-earmuffs.html

They do pretty well at keeping the wind off my ears.

Well, having bicycled through Finnish winters in our cold coastal regions, my tips should be helpful :)

When it's around +5 ... -5 C (41 F ... 23 F), I usually wear a thin bandana that covers the ears:

Then when it goes a bit lower, around -5 C ... -15 C (23 F ... 5 F), I wear a bit thicker fleece beanie which has no "band" in the bottom:

And then I loosen the helmet from the headsize adjustment so that it still fits fairly snugly and is not loose. You might also need to adjust the chin strap.

And for the real wintertime, between -15 C and -32 C (5 F ... -25 F) - the coldest I've bicycled in, but I didn't feel cold - I have the above fleece beanie and also a fairly thick wool pipe collar that starts from below the throat until all the way to the ears:

That keeps me warm :)

Also remember to dress in layers in wintertime:

• The bottom layer should be technical moisture wickening / merino wool


• The middle layer should be warm and slightly loose fleece


• The outer layer should be water and windproof but breathing, eg. goretex, softshell, etc.


• Two pairs of socks - thin moisture wickening and then wool socks :)


• Same for gloves: wool gloves and then water and windproof thick gloves where your index, middle, ring and pinky fingers are all in one "big finger".

And one more thing: Don't overdress! You will start sweating and then you'll feel miserable. Dress like you would when walking in 10 degrees C warmer weather. So if it's -25 C (-13 F), dress like you would in -15 C (5 F).

A completely different solution would be a thin but warm hat and a Hövding airbag collar. Not cheap, but I see plenty of people with that combination in Malmö, Sweden (probably because they’re a local company). Added bonus: it keeps your neck warm too.

Edit: hadn’t realised these were only for sale in Europe and Japan. I guess from OP’s “Northeast” that they mean north east USA, which might make this answer a little harder.

There are dedicated ear warmers to be attached to bike helmet straps (similar to those on ski helmets). There are photos on this blog post about "cat ears". I myself use hot ears. (I did note make a survey of all manufacturers that produce these. I just listed the first I found online).

Other than these, some bike fashion manufacturers produce dedicated thin hats to be worn under the helmet from some windproof fabric, that are cut out to cover the eary but leave enough of forehead and neck free, so you don't push it up when turning your head forward. I don't think though they are in practice much different than a buff.

With either (hot hears or under-helmet-hat) I'm not always satisfied as the helmet straps put very little pressure on them (from the side against the hat), so there is no force preventing a gap between head and tissue, through which the wind can blow in. I suspect that depends on the shape of your head, but in any case they are better than nothing. On very cold days I go with the combination under-helmet-hat + hot-ears which does a good job at sealing the ears from wind.

I use a "buff" almost all around the year in the outdoors - it is just a tube of cloth which you can wrap around your neck or different parts of your head, i.e. the ears, or neck+ears, or neck+ears+head+forehead, or neck+ears+mouth/nose. Very flexible. Should fit under any helmet, especially if you use it to cover not the whole head, but mainly neck/ears.

Also, ear muffs without the "bridge" part (trademark name seems to be "earbags"). Very nice, and may just be the right thing for your helmet, depending on its cut.

I use a set of earmuffs (eargrips brand) to bicycle in Montana winters. They fit below the helmet in the back. If you go for a helmet cover get one with some flair. I get smiles every time I ride with my Tail Wags dragon helmet cover. The covers are also great year round if your favorite helmet is starting to look faded.

Purchase a snowboarding helmet -- they are basically the same thing only fitted with internal insulation to .... keep you head and ears warm. It works great for me.

You can use a buff under the helmet and a wind (rain) cover over the helmet. I bike with this outfit during the winter and it keeps my head warm even with wind an snowy weather below -10 degrees C.