250 GSM is our everyday cold-weather standard — warm enough for winter city days, breathable enough for the trail.
Fabric weight guide
Which merino weight is right for you?
GSM is grams per square metre — how much fabric there is, not a warmth rating. Every weight is the same soft 17.5-micron Australian merino: it wicks sweat before it turns cold, insulates when it is cold and ventilates when it is warm. Lighter fabric breathes and dries faster; heavier fabric holds more heat when you stop moving. Choose by season and by how hard you will be working.
Warm & hot · 60°F+ / 15°C+
Best for: summer hiking, running, cycling, hot-climate travel, everyday tees and office wear; the next-to-skin layer under a 250 when you work hard in winter
Pick this if: you want a shirt that stays fresh for days, dries in an hour and keeps you cooler than cotton in the heat — or you simply run hot
Think twice if: you will mostly be standing still in the cold; on its own a lightweight layer has little insulation to offer
Shop 165 GSM →Cool to mild · 40–65°F / 5–18°C
Best for: spring and autumn as a standalone top, summer evenings, cool-morning hikes and commutes; winter as a base under a mid-layer
Pick this if: you want one merino layer that covers most of the year, or you are unsure between light and mid — this is where most people should start
Think twice if: you run cold and your winter is genuinely cold: go straight to 250
Shop 190 GSM →Cold · 20–45°F / −7 to 7°C
Best for: skiing and snowboarding, winter hiking, cold-weather work, frosty autumn mornings; top-and-bottom sets so your legs are not the weak link
Pick this if: you run cold in fall, want the classic winter base layer, or spend active days below freezing under a shell
Think twice if: you overheat easily on hard uphill efforts — a 165 or 190 underneath, 250 over it, is the better system
Shop 250 GSM →Deep cold · below 20°F / −7°C
Best for: ice fishing, hunting stands, camp at altitude, winter mornings spent waiting rather than walking, a house that never quite gets warm
Pick this if: warmth matters more than breathability, you are chronically cold, or your winter involves long spells standing still outdoors
Think twice if: you will be working hard — it is too warm for a sweaty climb, which is exactly the point
Shop 320 GSM →A base layer works by sitting close to the skin, where it can move moisture — loose is not more comfortable, just slower. Between sizes? Size down for a next-to-skin layer under a shell, size up to wear it on its own or over another layer. Merino stretches with wear and springs back after a wash. Heavier weight is not itchier: itch comes from coarse fibre, and every weight here is the same superfine merino.
Size guide
Size Guide
Our merino has a close, next-to-skin fit by design. If you are between sizes, stay true to size for base-layer use or size up for a more relaxed everyday fit. Free returns within 30 days, so ordering two sizes and sending one back is completely fine.
How to measure
Chest — around the fullest part of your chest, with the tape level under the arms.
Waist — around your natural waistline, with the tape comfortably loose.
Hips — around the fullest part of your hips and seat.
Inside leg — from the top of your inner thigh to your ankle bone.
Measure over light clothing, keeping the tape snug but not tight. Tap any chart below to open it full size.
Men's Base Layer Set
Need different sizes for the top and the bottoms? Build your own set →
Women's Base Layer Set
Need different sizes for the top and the bottoms? Build your own set →
Kids' Base Layer Set
Men's T-Shirt
Women's T-Shirt
Men's Long Sleeve
Same body measurements across 165, 190, 250 and 320gsm.
Women's Long Sleeve
Kids' Long Sleeve
Men's Long Johns
Women's Thermal Leggings
Kids' Thermal Leggings
Men's Half Zip
Women's Half Zip
Merino Wool Socks
Beanies, snoods and balaclavas
Still unsure which size to pick? Email info@merinotech.co.uk with your height, chest and waist and we will recommend a size. Free UK delivery over £49 and free returns within 30 days.
- Free UK delivery over £49
- 30-day free returns
- Ships in 1–2 business days
Description
Men's Merino Pants
Move freely with our Navy Men’s Merino Pants, engineered from nature’s finest performance fiber. Merino wool’s breathable thermoregulation adapts effortlessly to your body, while moisture-management technology keeps you dry through every activity.
Odour resistance ensures day-long freshness, and the elastic weave offers unrestricted flexibility. Soft to the touch and light as air, they’re the ultimate fusion of function and sophistication.
Complete with UV protection, antistatic balance, and eco-responsibility, these pants bring natural innovation to modern comfort.
Care
Turn inside out. Machine wash cold on a gentle cycle with like colours and a wool-safe detergent. Do not bleach. Lay flat or hang to dry — do not tumble dry.
Shipping & returns
Free UK delivery on orders over £49. Orders ship within 1–2 business days. 30-day free returns on unworn items with tags attached.
Men's base layer pants
The bottom half of staying warm
A soft merino legging with a wide comfort waistband and flatlock seams. Wear under ski pants, jeans or hiking trousers — or on their own at the cabin.
Size guide
Men's Pants 320
Fit
A close, next-to-skin fit made to sit smoothly under trousers, jeans and salopettes. Between sizes? Go by your waist measurement.
How to measure
- Chest – around the fullest part of your chest, tape level under the arms.
- Waist – around your natural waistline, tape comfortably loose.
- Hips – around the fullest part of your hips and seat.
- Inside leg – from the top of your inner thigh to your ankle bone.
Measure over light clothing and keep the tape snug but not tight. Still unsure? Email info@merinotech.co.uk with your height, chest and waist and we will recommend a size. Unworn items can be returned free within 30 days.
THE FABRIC
Why merino wool
Merino wool moves sweat away from your skin as vapour and lets it evaporate from the fabric, so you stay dry and comfortable whether you are hiking, commuting or skiing.
Merino fibres naturally resist the bacteria that cause odour, so you can wear a base layer for several days, on the trail or while travelling, and it still smells fresh.
Wool can absorb up to 30% of its weight in moisture without feeling wet. In damp British weather it keeps insulating where cotton and polyester leave you cold.
Merino absorbs UV radiation: our lightweight layers offer UPF 25 and the midweight and heavyweight options UPF 50+, handy on long days in the hills.
Merino wool is naturally hard to ignite and self-extinguishes without melting onto the skin, unlike synthetic base layers.
Merino is a natural, renewable and biodegradable fibre. Sheep grow a new fleece every year, and a worn-out merino garment breaks down instead of shedding plastic microfibres.
FAQ
Men's merino long johns: FAQ
What is this 320gsm thermal long johns best for?
It is a heavyweight 320gsm merino layer, best for deep cold, winter camping and ski days. Compare every weight in our merino weight guide.
Which sizes are in stock?
Available to order now: , M, L, XL. Our merino is true to size and designed to sit close to the skin; see the size guide for measurements.
Is this thermal long johns warm enough for skiing?
Yes. 320gsm heavyweight merino is our warmest weight, ideal under ski clothing in very cold resorts or if you feel the cold.
What are merino base layer bottoms used for?
Merino long johns are thermal leggings worn under trousers, salopettes or waterproofs. They trap warmth, move sweat away from your legs and stop the cold, clammy feeling that cotton leaves behind, whether you are skiing, hillwalking, fishing or working outdoors.
Which weight of merino long johns do I need?
165gsm for mild days and high-output sports, 200gsm for cool UK weather and layering under jeans, 250gsm midweight for most winter activities including skiing, and 320gsm heavyweight for severe cold or standing still for long periods.
Can I wear merino thermal leggings under jeans or work trousers?
Yes. The fabric is thin for the warmth it gives and the flatlock seams lie flat, so they sit comfortably under jeans, chinos and work trousers without bulk.
How should merino long johns fit?
Snug from waist to ankle so they wick properly and do not bunch under other layers. They are true to size; check your waist and inside leg against the size guide.
Should I buy a matching top?
A top and bottoms in the same weight give the warmest, most even layering. Buying them as a base layer set costs less than two separate pieces, or you can mix weights in the set builder.