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I've heard many people like to use plastic newspaper bags or grocery bags as a vapor barrier when cold weather cycling. I'm already wearing winter cycling boots which prevent outside water infiltration, but I've been considering this for really cold days or longer rides below freezing since my insoles eventually get soaked with sweat eventually and become very good at transferring the cold from the bottoms of my shoe to my feet.

What is the most effective way to use vapor barriers inside shoes to keep warm? Should I wear the vapor barrier over my socks, under my socks, or between two layers? What is the theory behind it?

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I tried this for Scout winter campouts, etc, and found it impossible to walk, because the plastic makes your foot slide around in the shoe. Others swear by the technique, though. (The main idea is that it prevents evaporative cooling of the foot.) –  Daniel R Hicks Feb 22 at 3:21
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What kind of temperatures and wind are you dealing with and are you wearing wool socks? (contrary to popular belief, wool socks are not made of wool, but of magic warm keeping ness) –  Batman Feb 22 at 7:40
    
Most times it's 20f to 30f, but it has been dipping down to -5f or so occasionally so due to to the polar vortex. And yes, always wearing wool. –  Benzo Feb 22 at 20:32
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I used neoprene socks successfully while riding deep snow in the alps. Although your feet will become wet, they will stay relatively warm. –  arne Feb 24 at 8:13
    
I am very much with @arne I've seen people developing various sorts of feet-things (where I lack proper medical names as non-native speaker) after several hours of sweat bathing in a 100% tight vapor barrier. There are various types of "water proof" socks that allow your feet to stay "somewhat" dry without leaving them cold from the energy spend on evaporation of water (which is the theory in a few words). –  StefG Feb 26 at 6:53

4 Answers 4

I rode a couple winters as a bike messenger in the northeastern US, and this is a classic messenger trick for the worst cold wet days. While your feet may still become somewhat wet, at least they will be warm and wet. I liked wearing a thin sock on the inside, the plastic bag, another pair of socks, then shoes.

This is not really a dry-day technique. Then, as @hillsons said, you will just have wet feet for no reason. When it's dry and really cold, put flat pedals on your bike and wear normal civilian winter footwear. Hiking boots, for example. But when it's 35 degrees and raining and you are silly enough to be on your bike, the plastic bags trick is the way to go.

One place to search advice on vapor barriers is in the camping/backpacking world, there's been plenty of experimentation with them since at least the 60s in that community.

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I have used this technique in emergencies while hiking, but never thought of deliberately using it day-to-day.

When the weather unexpectedly turns foul (and this is before I had the money to buy quality waterproof hiking shoes), my feet would soak. So I would takeout a thick plastic bag from the backpack.

  • Put dry socks on.
  • Put the plastic bag over them, but leave a lot of space in front of the fingers. Otherwise when putting on the shoe, and when walking, the toes tear the plastic bag.
  • Put the wet sock over. This will prevent the plastic bag of sliding against the shoe and tearing.
  • Put the shoe on.

So this works for several hours (with increasing levels of discomfort) and keeps the feet dry-ish in an emergency. However, the feel is slippery (on every step, the socks slip a bit). Really not my idea of "fun".

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A rehash of a previously posted answer, but I wear socks with SPD sandals in the wintertime. I can pile up as many layers of wool socks as I need for the day's temperature conditions, and just adjust the straps on the sandals to make room for the extra bulk. The plastic grocery bag I put between the outermost and next inner layer of sock. I've done this, had my feet soaking wet yet still toasty warm in temperatures as low as -20F.

They key though is that you need to select your footwear to target about 20-30 degrees warmer than the ambient air, so that you are not sweating when biking. If you are standing around doing nothing, your feet should be cold.

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Woudld love to see a picture to better under stand. Never seen SPD sandals before. –  sixtyfootersdude Feb 26 at 0:05

It's not actually that cold, so a decent pair of old-fashioned non-breathable leather boots or hiking shoes with 2 pairs of socks should be enough, 3 pairs at the very lowest temperatures you mention.

Hiking trainers + 1 pair of warm socks is fine down to -6C (21F) for me in the dry, so long as I keep the wind off my ankles.

If you do go for a vapour barrier, you need enough packing (in the form of socks) in there that your feet don't move around - another reason for boots over shoes, even if just ankle boots.

A grippier option may be replacement latex socks for a drysuit - with only thin socks underneath and thick on top if needed, plus they're generally quite long.

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