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Wool or Cotton Hoodie for a Canadian Winter?

Wool absorbs more moisture and gives off more heat than cotton, but the effect is brief. What the research shows, and how to read a Canadian fibre label.

Every October the same question turns up. The heating's on, the first frost has been and gone, and you're standing in a shop holding a heavy cotton hoodie in one hand and a wool one in the other. Which one is warmer once it's minus ten and you've been walking for twenty minutes?

The honest answer is shorter than most of what's written about it. Wool does one thing cotton does less of, and that thing matters in some winters and barely registers in others. Here's what the evidence says, and what it doesn't.

Both fibres drink water vapour

Wool and cotton are both hygroscopic. They pull water vapour out of the air and hold it inside the fibre, not just on the surface. That's the big difference from polyester, which takes up very little. The question is how much each one holds and what happens when it does.

The Woolmark Company, the wool industry's own marketing and research body, says in its fact sheet Wool is naturally breathable that wool can absorb up to 35% of its weight before it feels wet. Treat that as an industry figure, because that's what it is. The same fact sheet compares wool mostly with synthetics and polyester. It doesn't put a matching number on cotton.

You'll see tidy regain figures for both fibres quoted all over the internet, often sourced to ASTM International. Be careful with those. ASTM D1909, Standard Tables of Commercial Moisture Regains and Commercial Allowances for Textile Fibers, lists regain values for fibres, but ASTM's own summary says each value "is not an experimentally determined quantity but a purely defined value arrived at for commercial purposes." Those numbers exist so mills can agree what a bale of fibre should weigh when it's bought and sold. They aren't a measurement of how a finished hoodie behaves on your back.

The warm part: heat released when fibre takes up moisture

When a hygroscopic fibre absorbs water vapour, it gives off a small amount of heat. This is the bit of the wool story that's real physics, not folklore. Walk out of a dry, heated flat into damp November air, and a wool layer will warm slightly as it takes on moisture.

A 2026 paper in the journal Fibers, Measuring the Heat of Wetting of Clothing Fabrics by Isothermal Calorimetry by Faisal Abedin and Emiel DenHartog, measured this at fabric level rather than fibre level. They tested merino wool, cotton, viscose and polyester fabrics in a microcalorimeter at 23 °C. The order was clear:

  1. Wool gave off the most heat.
  2. Viscose came next.
  3. Cotton came after that.
  4. Polyester gave off almost nothing, because it barely absorbs moisture.

Two things keep this from being a knockout. First, the authors found the fabric-level values were lower and more variable than the fibre-level figures in older literature, because weave, air gaps and how the sample was cut all got in the way. They describe their method as showing both what calorimetry can do and where it falls short. Second, the work was funded by Australian Wool Innovation, which owns the Woolmark Company. That doesn't make it wrong. It's a peer-reviewed paper and the ranking matches basic fibre chemistry. But you should know who paid for it.

The Woolmark Company also reports on a wider dynamic breathability project, a four-year PhD at North Carolina State University, with sweating manikins and people wearing wool, cotton, viscose and polyester garments of similar weight and thickness. Woolmark's summary says wool kept people feeling warmer during rest phases, after activity. That's the wool industry's own summary, so read it as such.

What the research doesn't settle

None of this tells you which hoodie wins at a bus stop in Winnipeg. The lab work runs at room temperature, in controlled humidity, over short time windows. The heat from absorbing moisture is a short-lived effect. Once the fibre has taken up what it's going to take up, it stops. It's a buffer, not a heater.

What decides warmth on a cold day is mostly duller stuff:

  • Still air. Thickness and loft trap air, and trapped air is what insulates. A dense 500 gsm cotton hoodie and a thin wool jumper aren't a fair fight in either direction.
  • Wind. Neither a knit cotton nor a knit wool stops much wind on its own. The shell over the top does that job.
  • Sweat. If you overheat on the walk and soak the layer, then stand still, you'll get cold in either. Wool handles that stop-start pattern somewhat better, according to the research above. Cotton holds the water and dries slowly.
  • Fit. A mid-layer that's skin-tight under a coat compresses its own loft. One that's too loose lets warm air pump out at the hem.

If you want the cotton side of the fabric question in more detail, we've covered loopback terry versus brushed fleece, which changes how much air a cotton hoodie traps far more than people expect.

So which one, honestly

Pick by the winter you actually have, not the one in the advert.

Cotton makes sense when

  • Your cold is mostly dry and short. Car to office, flat to shop, a twenty-minute walk with a decent coat on top.
  • You want something you can throw in the machine every week or two without a separate routine. Heavy cotton handles a normal wash. Most wool needs a gentler cycle or hand washing, and a felted wool hoodie can't be undone.
  • You want the thing to take abuse at the cuffs, elbows and pocket edges and still look like itself after a few winters.

Wool makes sense when

  • You're out for hours, working hard and then stopping. Shovelling, winter hiking, a site job, walking the dog in the dark for an hour.
  • Your cold is damp. Coastal BC, the Maritimes, slushy March days in southern Ontario.
  • You're willing to wash it less often and more carefully.

Whatever you pick, the hood counts too. We looked at whether putting your hood up actually keeps you warm.

How to read the label in Canada

This is where you can stop guessing. The Textile Labelling and Advertising Regulations under the Textile Labelling Act set out what a fibre content label has to say. A few rules worth knowing in the shop:

  • Percentages by mass, in order. Section 31 says every fibre at 5% or more must be shown by its generic name, with its percentage, in order of how much of it there is. Smaller amounts can be grouped as "other fibre" or "other fibres".
  • A 5% tolerance on blends. Under section 30, a labelled percentage can be off from the real one by no more than five per cent. So "60% wool, 40% cotton" can be a little either side of that.
  • "Wool" is the regulated name. Section 26 sets the generic name for fibre from sheep or lambs as "wool". Words like merino or lambswool on a hang tag are extra description. The fibre content line is the part to read.
  • Recycled wool has to say so. Section 33 requires "reclaimed", "reprocessed" or "reused" immediately before the generic name when the fibre is reclaimed. Section 41 treats calling reclaimed fibre "virgin" or "new" as misleading unless the contrary is proven.
  • "All" and "pure" mean one fibre. Section 29 lets a label say "all" or "pure" in place of 100% only when a single fibre makes up the content, with narrow exceptions for small amounts of elastic, reinforcement or ornamentation that the label has to declare.

The short version

Wool absorbs more water vapour than cotton and gives off more heat when it does, and peer-reviewed fabric testing backs that ranking. The effect is real, brief and smaller at fabric level than the fibre figures suggest. Most of the evidence comes from work the wool industry paid for. For long, damp, stop-start days, wool has a genuine edge. For the daily round in dry cold, a heavy cotton hoodie under a proper shell does the job and takes a beating doing it. Read the fibre content line, not the hang tag, and if you're going cotton, our washing and care instructions will keep it going for a lot of winters.

Sources

PreviouslyShould You Hang a Heavy Hoodie or Fold It? NextCotton or Cotton-Poly for a Heavy Hoodie?
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