Sounds like dark magic, doesn't it? A fabric that can keep you both warm and cold, depending on the situation.
Well, that's just one of the characteristics that makes merino wool a wonder fabric.
So, this is how merino keeps you warm when you need to be warm and cool when you need to be cool.
Firstly, there are a few ways how merino keeps you warm.
The merino wool fibres have a crimp to them which creates pockets that trap warmth. The warmth gets trapped to keep you warm.
And, merino wool can absorb 30% its weight in moisture (for a 180 gram tee that's 60 grams/60 milliliters of sweat or rain water). This moisture is then readily 'wicked' or evaporated into the air. Think cotton for a moment. We've all been stuck in a wet or sweaty cotton tee, right? Takes yonks to dry. If you're starting in a chilly breeze admiring the view in a soggy cotton tee you're going to feel cold. In merino the moisture is readily evaporated so you don't have that experience.
So that, in a nutshell, is how merino wool keeps you warm.
But how does merino keep you cool?
Partially it's down to the fact that merino wool is extremely breathability—it doesn't act as an impermeable barrier in the same way that, say, a rain coat does. Wear a rain coat in even really chilly conditions and work up a sweat—you'll feel hot. (As I write this, a few days ago I went on a day hike in the Blue Mountains and it was in the single digits. I wore a short sleeve merino tee and my shell and that was more than enough to warm up.)
The other aspect of how it keeps you cool is the moisture wicking characteristics of merino wool. Your sweat is trapped in the fabric which then evaporates into the air and sort of acts like an evaporative cooler. And the beauty here is you don't feel soggy and gross in a sheet of your own sweat in hot conditions like you would in cotton.
I like the way Woolmark describes merino wool in the context of how it keeps you warm and cool. "Merino wool is an active fibre that reacts to changes in body temperature."
It may still sound like witchcraft but never fret: merino is the best fabric for warm and cool conditions. The most intrepid adventures from across the world will vouch for this.
While we've got you, check out our other blog on why a long sleeve merino tee isn't just a go-to for winter, but makes a great summer hiking top too.