Every winter we get the same question: which thermals should I buy? The honest answer is that the best merino thermals depend on what you're doing and where. A 2am toilet trip at a Victorian Alps campsite is a very different job to a brisk morning on the Larapinta. Here's what to look at, in the order it matters.
1. Fabric weight (gsm)
Merino weight is measured in grams per square metre, or gsm. It's the single best guide to how warm a thermal will be.
- Around 150gsm (lightweight): a thin layer for active days in cool weather, or for people who run hot. Breathes well, packs small, but won't do much on its own at camp.
- Around 200 to 230gsm (midweight): the all-rounder. Warm enough to sleep in and wear around camp, light enough to hike in on a cold morning. This is where most Australian hikers end up.
- 260gsm and up (heavyweight): for snow, alpine winters and people who feel the cold badly. Very warm, but you'll overheat in it once you start walking uphill.
Our thermals are 210gsm. We chose midweight because most Aussie hiking and camping sits between a frosty morning and a mild afternoon, and one good layer is better than three you never use.
2. Pure merino or a blend
You'll see thermals sold as "100% merino", and others blended with elastane, nylon or polyester. Each has a job:
- Elastane (a few percent): gives stretch and helps the thermal spring back into shape, so knees and elbows don't bag out after a day.
- Nylon: adds strength. Useful in leggings and high-wear areas, at the cost of a little softness.
- Polyester or other synthetics: usually there to bring the price down. They dry faster, but they hold onto smell much more than wool.
Our thermals are 95% Australian merino and 5% elastane, so they stretch and recover but still feel and smell like wool. If you want to dig into this, we wrote more about 100% merino vs merino blends.
3. Micron (how soft it feels)
Itchiness comes from thick fibres, not from wool itself. Look for superfine merino, which is 18.5 micron or finer. Ours is 18.4 micron. If you've had itchy wool before, read is merino wool itchy? before you rule it out.
4. Fit
Thermals work by trapping a thin layer of warm air against your skin, so they should sit close without squeezing. Too loose and the warm air escapes; too tight and they'll restrict you and wear faster at the seams. Check the size chart rather than guessing from your T-shirt size. Ours is on the size chart page.
Two things to check on the top: a longer body, so it stays tucked in when you bend and reach, and sleeves long enough to reach your wrists when your arms are out in front of you.
5. Top, bottoms or both?
If you only buy one, buy the top. Your core loses the most heat and a thermal top layers under everything. Add bottoms if you camp in winter, hike in alpine areas, or sleep cold. Thermal bottoms make a bigger difference in a sleeping bag than most people expect.
6. Where it's made
"Australian merino" on a label usually tells you where the wool was grown, not where the garment was made. A lot of Australian wool is shipped overseas to be spun, knitted and sewn. If you'd like your thermals made here, look for the green-and-gold Australian Made logo, which is independently licensed. We knit, dye and sew our thermals in Melbourne, and our wool is mulesing-free and RWS certified.
7. Care
Merino thermals last for years if you treat them right. Wash warm on a gentle or wool cycle (or by hand), skip the dryer, and dry flat in the shade. Don't use bleach or enzyme detergents. If one does go wrong, here's how to try to rescue shrunk merino.
How we'd layer them
On a cold hiking day: thermal top under a merino hiking shirt or fleece, with a shell over the top. At camp: add the bottoms and a puffer. We go through it in more detail in how to layer for winter hiking, and you'll find thermals on our Three Capes and Larapinta packing lists.
Quick answers
What gsm merino thermals should I get for hiking in Australia? For most people, midweight, around 200 to 230gsm. Go lighter if you run hot or mainly wear them while moving, and heavier for snow.
Can I sleep in merino thermals? Yes. That's one of the best uses for them. Merino stays comfortable across a wide range of temperatures and doesn't get clammy like synthetics.
How many days can I wear them? Several. Merino resists odour, so on a multi-day hike one set is usually enough. More on that in how long can you wear merino without washing.
Our men's and women's thermal tops and bottoms are $110 each, made in Melbourne from 18.4 micron Australian merino. Have a look at the men's thermals and women's thermals.
