The Benefits of Wearing Merino Thermals

So you’re preparing to hike the Overland or Routeburn Track. You’re poring over various gear lists to work out what you need to pack. Every list recommends thermal underwear, preferably made from merino wool. But why? Why not just wear an extra heavy jumper if it’s cold during the day, or your favourite trackies in your sleeping bag at night? 

Well, there’s a reason why thermals are on every gear list. Here are the main benefits of merino thermals: 

Merino Thermals Trap Heat

You know how thermals tend to sit really close to the skin? That’s on purpose. It’s to trap heat.

Thermals are generally available in different weighs from 180GSM for mild conditions all the way up to 300GSM for the seriously chilly stuff. GSM, by the way, stands for grams per square metre. Grams of fibres—in our case merino fibres. So, naturally the higher the GSM the warmer they are, but still on the principle of being worn close to the skin to trap warmth. 

Which brings us to the next point… 

Merino Thermals Aren’t Bulky

Merino thermals do their work keeping you warm not by being bulky but by trapping the heat. This is beneficial on the track as it allows you to stay nimble. 

Hiking your way up to Mackinnon Pass on the Milford dressed like Michelin man wouldn’t be a pleasant experience. In fact, look at the down jumpsuits that the Everest climbers wear. They’re wearing what are effectively sleeping bags due to the sheer cold. And, they haven’t got a lot of dexterity about them as they laboriously plod their way to the top. 

Fun fact: Richard is wearing several layers here. On top he's wearing a thermal base layer—an Ottie Merino Men's Merino Thermal Top—a lightweight Ottie Merino Long Sleeve T-Shirt over the top, and a shell/raincoat. It was an especially cold day on the Routeburn Track and even when hiking at a decent pace we were cold. "But Paul, why wear 2 tops when you can just wear a fleece?" Well, options. The more options you have on the track, without taking your entire wardrobe, the better. We originally carried the thermals as a 'just in case' but ended up wearing them the whole time. If we got too warm, we could simply remove a layer. Heavy, bulky layers are kind of like putting all your eggs in one basket. 

At lower altitude in milder conditions we don’t need to go to that extreme. If it’s really cold on the track we can wear non-bulky layers that keep us warm by trapping heat while allowing us to move freely. 

What’s more, when your thermals are in your pack they’re not going to take up much room. And this is why I tend to carry two sets with me on a big hike if the forecast is looking chilly. A full set—merino thermal top and bottoms—to wear during the day if need be, that can get dirty and wet and be aired to dry in the tent or hut at night. And a spare set to wear around camp as my pyjamas. If conditions are looking milder and like I might only need them at night, I’ll take one set. 

Merino Thermals Are Lightweight

Merino thermals are lightweight. They don’t take much room in the pack, nor do they weigh much in the pack. 

A men’s merino thermal top in a 200GSM weight fabric will roughly take 1.15sq/m of fabric, and thus will weigh just over 200 grams. 

Merino Thermals Sport All The Benefits of Merino

I won’t rehash too much what these are—we’ve written about the top 7 benefits of merino here. But, damn straight merino thermals possess them too. 

Odour resistance—you can get away with wearing the same pair for multiple days without smelling offensive. Moisture wicking—as you sweat, they wick. They dry quick. They breathe. And so on… 

So all this is why merino thermals appear on most gear lists you’ll see for multiday hikes. Regardless of conditions, it’s always a good idea to have a set in your pack just in case. After all, they are not bulky and don’t weigh much. 

Looking to grab a set of thermals? We're currently clearing our stock for up to 45% off!