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Does Putting Your Hood Up Actually Keep You Warm?

Does a hood keep you warm? What a Manitoba study found about head heat loss, what a hoodie hood does, and how to wear one in a Canadian winter.

October is when the hood starts going up. The first morning at 2°C with a wind coming off the lake, you pull it over your ears without thinking. Somebody says you lose half your body heat through your head. Somebody else says that's a myth. Both are half right.

The short answer

Yes, putting the hood up keeps you warmer, but not for the reason usually given. Your head doesn't leak heat out of all proportion to its size. In the best controlled test we could find, it lost heat roughly in line with how much skin it has. It helps because by October the rest of you is covered, so a bare head and neck become a big share of the heat you're still losing. Cover them and you've shut one of the last open doors.

Where the "half your heat" idea falls down

The clearest test comes from the University of Manitoba. In a 2006 study in the Journal of Applied Physiology, Thea Pretorius, Gordon Giesbrecht and colleagues put eight healthy men in 17°C water, with the head either above the surface or fully under it, and the body either insulated or bare. Shivering was suppressed with medication so it wouldn't muddy the measurements.

The submerged head was about 7% of body surface area. Putting it under raised total heat loss by about 10%. In the authors' words, the head "does not contribute relatively more than the rest of the body to surface heat loss." The head as a chimney doesn't survive the data.

Why a cold head still matters more than its size

The same study found something less tidy. Cooling the head made the core cool much faster than the extra heat loss would predict. Across conditions, the core cooling rate rose by an average of 42% while total heat loss rose by about 10%. Even with the body wrapped in insulation, submerging the head dropped core temperature by 0.77°C over 30 minutes, against 0.47°C with the head kept out.

The authors' explanation is that cold on the scalp, face and neck prompts the body to pull blood away from the surface, so the heat that does escape comes out of a smaller warm core. They also cite earlier work showing that blood flow to the head is 4 to 10 times higher, relative to its surface area, than in the trunk and upper limbs, and that scalp vessels barely narrow in the cold. Your fingers go white in the cold to save heat. Your scalp doesn't.

Two caveats. This was water, which pulls heat away far faster than a breezy sidewalk. And it was eight men in a lab with shivering switched off. It shows how the head behaves, not how much warmer the bus stop feels.

Why it feels like your head loses so much

Environment Canada's wind chill factsheet tells people to wear a hat because "we lose a large portion of our body heat from the head." On a cold day that's often true in practice, because the head is the part left bare. With your torso under a hoodie and a jacket, legs in denim and hands in pockets, most of the skin facing the air is face, ears and neck. A large portion of a small total is still a large portion.

The same factsheet says the ears, nose, fingers and toes lose heat fastest, and its own wind chill example is how cold your face will feel. Ears and neck are exactly what a hood covers.

What a hoodie hood actually does

A hoodie hood isn't a fitted toque. It's a loose shell of the body cloth, open at the front, and it does four things.

  • It covers the ears and the back of the neck. They sting first in a cold wind.
  • It holds still air. The factsheet explains that wind strips away the thin layer of warm air next to your skin, and that good insulating clothing works by trapping air and thickening that layer. A hood keeps a pocket of still air around the head even where it doesn't touch.
  • It closes the neckline. With the hood down, the collar is open and warm air rises straight out of it. With the hood up, neck and head become one covered space.
  • It leaks at the face. The opening faces the way you're walking, so a headwind goes straight in. Pull the drawcord in a few centimetres and the opening narrows to your face.

How much insulation a hood adds, in clo or any other unit, isn't something we can tell you. Swedish researchers had six people estimate the insulation of multi-layer cold weather outfits using the summation method in ISO 9920, the international standard for estimating clothing insulation, and compared the estimates with thermal manikin measurements. In Gavhed, Kuklane and Holmér's 2000 paper, the small items (helmet, gloves, socks and hood) gave the widest spread between raters, with coefficients of variation from 23% to 73%. If trained raters can't agree on a hood from a table, a warmth figure on a product page wouldn't mean much. A heated manikin is the honest route to a number.

What to check on a hood before winter

With no reliable warmth figure to go on, judge a hood by the four things above. Put it up in front of a mirror.

  • Depth. The front edge should sit past your ears and stay there when you turn to check traffic.
  • The cord. It should run freely and close the opening without bunching the hood. If one's gone missing in the wash, here's how to get a drawcord back into a hoodie.
  • The cloth. The hood is part of the same layer of trapped air as the body. A thin hood on a heavy hoodie is the weak spot.
  • The neck. With the hood up, the front of the neck should be covered, not left open by a deep gap under the chin. That gap lets the held air out.

Getting the most out of the hood

  1. Up before you're cold, down before you sweat. Health Canada's extreme cold guidance says to remove layers if you get too warm, before you start sweating, and to change out of wet clothing because you lose heat faster when you're wet. Hood down on the climb, back up at the top.
  2. Use the cord. Snug, not strangled. A few centimetres closes most of the gap at the face.
  3. Wear it under the jacket hood, not over the jacket. Hoodie hood up, jacket zipped, jacket hood over the top. Health Canada's advice is layers with a wind resistant outer layer. Heavy cotton holds air but isn't windproof, so let the jacket take the wind.
  4. Add a toque underneath when it really drops. A hood sits off the head, a toque sits on it. That's two layers on the scalp and ears, with the wind kept off the toque. Environment Canada says frostbite risk rises rapidly once wind chill goes below -27, and at that point the advice is to cover as much exposed skin as possible. Health Canada adds a scarf over the nose.
  5. Keep the hood dry. The factsheet notes that wet clothing loses its insulating properties, with heat loss nearly equal to that of exposed skin. A cotton hood soaks through in sleet. When it comes home wet, here's how to air dry a heavy hoodie without it going musty.

What the evidence doesn't settle

We didn't find a study that measured a hoodie hood on a person walking in Canadian autumn air. The Manitoba work is cold water, and the Swedish paper is about estimating insulation, not hoodies. Here's where things stand. "Half your heat goes out through your head" is folklore. "The head loses heat roughly in proportion to its surface area" is supported by one careful study. "Covering your head matters once the rest of you is dressed" follows from simple arithmetic and Canada's own cold weather advice. How many degrees a particular hood is worth is still open, and anyone who quotes you a figure should be able to show you the manikin test behind it.

A hood worn hard all winter gets washed a lot. Our care notes cover how to keep the cloth thick and the cord where it belongs.

Sources

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