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 Wool Thermal Set
Built for durability and comfort, this Men’s Merino Wool Thermal Set is ideal for everyday winter wear and outdoor activities. The fabric naturally regulates temperature to maintain warmth while remaining breathable enough for indoor comfort. Moisture-wicking technology helps keep the body dry during movement and active use. Natural odour resistance prevents unpleasant smells, while soft hypoallergenic wool provides smooth irritation-free comfort.
Lightweight elasticity improves flexibility and ease of movement. Anti-static performance reduces cling in dry weather, while UV protection and eco-friendly renewable wool fibres support long-term wearability and sustainability.
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 set
Top and bottom, matched and ready
Long sleeve top and pants in the same weight and colour — the fastest way to a complete cold-weather base. Flatlock seams, a soft non-itchy finish and a fit that stays close without squeezing.
Size guide
Men's Set 165
Fit
The top and the bottoms come in the same size, with a close, next-to-skin fit. Need different sizes for the top and the bottoms? Build your own set.
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 thermal sets: FAQ
What is this 165gsm thermal base layer set best for?
It is a lightweight 165gsm merino layer, best for running, cycling, travel and layering. Compare every weight in our merino weight guide.
Which sizes are in stock?
Available to order now: , S, M, L. Our merino is true to size and designed to sit close to the skin; see the size guide for measurements.
Is this thermal base layer set warm enough for skiing?
It works for spring skiing, ski touring or as a thin layer under a warmer mid layer. For a standard winter ski week, most people choose 250gsm.
What is included in a merino base layer set?
A long sleeve thermal top and matching long johns in the same fabric weight and colour, so your core and legs stay equally warm.
Is a set cheaper than buying the top and bottoms separately?
Yes, a set is priced below the two pieces bought individually. If you want different weights or colours for the top and bottoms, use the build your own set page.
Which merino set is best for skiing?
For most skiers in the Alps or Scotland a 250gsm midweight set is the right choice. Choose 320gsm if you feel the cold, ski in very low temperatures or spend long periods on chairlifts, and 165–200gsm for spring skiing or ski touring.
What is the advantage of a zip-up set?
The half-zip top lets you vent heat quickly on climbs or in a warm lodge without taking a layer off, then zip up again when you stop.
How do I choose the size for a set?
Top and bottoms come in the same size, which suits most people. If your top and bottom sizes differ, build your own set instead. Measurements are in the size guide.
I am 5.10 ft with 77 KG of weight. Size M fits really well.Still not to try how it works in Cold weather but the built quality is very good. I took 320g set and its not very thin and has some weight so I think I got what I purchased (more Wool)I am feeling some itching when wearing without any undergarments on top so I think I need to use it wearing something below.Feels like I am set for USA Winters
I am 5.10 ft with 77 KG of weight. Size M fits really well.Still not to try how it works in Cold weather but the built quality is very good. I took 320g set and its not very thin and has some weight so I think I got what I purchased (more Wool)I am feeling some itching when wearing without any undergarments on top so I think I need to use it wearing something below.Feels like I am set for USA Winters
Very good quality for a good price, although the product doesn't have the Wool Mark certification logo it is made well, might have to test the purity of the wool the old fashioned way, burning and sniffing a bit of the lint ;)
the seller even threw in a free pack of socks!
Very good quality for a good price, although the product doesn't have the Wool Mark certification logo it is made well, might have to test the purity of the wool the old fashioned way, burning and sniffing a bit of the lint ;)
the seller even threw in a free pack of socks!
These are the absolute best long johns!
These are the absolute best long johns!
Excellent product and fast shipping but I was charged for sales tax and there is no sales tax on clothing in Minnesota.
Excellent product and fast shipping but I was charged for sales tax and there is no sales tax on clothing in Minnesota.
It’s really working , recommend for everyone who go outdoors
It’s really working , recommend for everyone who go outdoors
I bought it for my son for Christmas. Did not try it yet. I like its quality. It is soft and warm.
I bought it for my son for Christmas. Did not try it yet. I like its quality. It is soft and warm.
Gift
Gift
A gift. fast shipping. I also own a pair that I love. well made. Fast shipping. as described.rlw
These are the best long John’s I’ve ever used, fit great and really keep you warm in cold weather!
Good fit works well can't get the discount from the voucher they send in the packet it's only for US and Canada I did try and email no luck with getting any discount, they should tell you that in the add. Shame I would have got more from them 😕
A gift. fast shipping. I also own a pair that I love. well made. Fast shipping. as described.rlw
Good fit works well can't get the discount from the voucher they send in the packet it's only for US and Canada I did try and email no luck with getting any discount, they should tell you that in the add. Shame I would have got more from them 😕
These are the best long John’s I’ve ever used, fit great and really keep you warm in cold weather!
Would purchase again.
Would purchase again.
Excellent
Good quality for the money.
Good quality for the money.
Excellent
I wasn't sure about this but took a chance. I'm pleased about the quality of this thermal underwear. I tested it out the other day and was very comfortable without being itchy. It was an added bonus to get the pair of Merino socks as well. This was first class all the way.
It’s hard to trust sizes nowadays, however after checking my measurements I was a size medium, usually with cotton I’m a size large..needless to say so far I have worn them together just about every night to bed, I am not to cold nor do I sweat profusely under the covers. Being a little on the low iron side these have been my best friend since arrival!The only negative I have so far is that it’s made in China, hear me out China can and does make some stellar products however most items that come from there are poorly designed and made with cheap or inferior materials. Neighboring countries have far better standards and qualified seamstresses that make a far superior stitch. I’m giving a 4 star review for the time being waiting on the length of time it takes to see if they will hold up to the test of time for a very very active individual..
I wasn't sure about this but took a chance. I'm pleased about the quality of this thermal underwear. I tested it out the other day and was very comfortable without being itchy. It was an added bonus to get the pair of Merino socks as well. This was first class all the way.