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Best Cold Weather Baselayer

The Brynje Super Thermo Shirt with shoulder inlays

Brynje's Super Thermo Baselayer with Shoulder Inlays


As always, we're looking at the Brynje Super Thermo mesh baselayer from the point of view of long distance trekking over tough terrain.

For more information around the concept and purpose of the baselayer see this archived review.  

Test subject: Chest 42", Waist 33", Height: 5ft 8"
Test item: Green, size = Extra Large (Large would have been fine)
Kit Tests: Winter
Disclaimer: None required (item not provided by manufacturer)


Materials: Polypropylene Mesh 100%
Fabric Weight 140 g/sm
Weight (measured - Size XL / stated - with no size reference) 160g / 140g
Product Sizing Reference: 42" Chest = Large
Manufacturer RRP (LS Version) ~£50.00
Manufacturer RRP (SS Version) ~£39.00

Manufacturer's Page


Scramble Review




Embracing the Poly

High quality merino-synthetic hybrid baselayers are really two-layered items in one (a synthetic next-to-skin hydrophobic layer and a more absorbent natural wicking layer). In this review we're looking at pulling these two layers apart; the Brynje shirt being the next-to-skin layer working in conjunction with an existing 3-season baselayer or zipped tee instead of using a traditional mid. So we're looking at the Brynje baselayer as a durable sub-zero component in a flexible, modular, 4-season baselayer set.

We've advocated for three next-to-skin layers for all-round use:

  1. A sub zero option: (Category = "Cold Weather LS Baselayer Top")
  2. A 3-season baselayer: (Category = "Lightweight (3 Season) LS Baselayer Top")
  3. A loose summer zipped tee: (Category = "Trekking SS T-Shirt")

With the Brynje mesh baselayer, we're looking at integrating it with options (2) or (3) depending on conditions (see below).

Why the shift in focus?

Every year the price of merino baselayers jumps in not inconsequential leaps. Not many years ago the RRP of a good quality merino-synthetic mix (polyester or polypropylene) baselayer was around £50 (and on sale you might pick one up for £30), now these RRPs are hovering just below £100 and it's forced us to be somewhat apologetic in advocating their use. So we decided to test a different approach.

Some people say not to worry about the air

The mesh concept is not new and the company that has become synonymous with high quality mesh layers is Brynje. Tenzing and Hillary climbed Everest wearing Brynje baselayers and Brynje have been trapping air in little squares since 1921 but it wasn't until the late 1950's that polypropylene began to be used in textiles; and it was this adoption that really transformed a string vest into a performance baselayer. We've long espoused the wondrous properties of polypropylene for baselayers (see postscript below), so this winter we decided to see if we could escape the pricey flock and embrace some mid-20th century fishnet tech.

The mesh idea is simple and Brynje sum it up rather well:

At times of high activity, the mesh ensures air circulation and transports excess moisture and heat away from the body. At times of low-intensity activity or during periods of rest, the mesh cells retain warm air and form an uninterrupted insulating layer next to the skin.

Combining the Brynje shirt with an additional fitted layer is very similar to creating a more robust and more aggressively hydrophobic version of Montane's Allez Micro baselayer for harsh sub-sero conditions.  Brynje emphasise the use of a 3-layer approach and many might combine theirs with a mid-layer, however we think instead of a mid-layer (which tend to be overly warm) an additional fitted, hydrophobic baselayer is better (such layers are designed to move moisture via capillary action and aid moisture transport away from the skin). In the 2023 winter kit test I wore the Brynje shirt under a Megmeister Drynamo and wore a Mountain Hardware Hooded Chockstone softshell as the third (outer) layer (unless a hardshell was required).

Let's take a quick tour of the Brynje Super Thermo and then we'll talk more about how it performed and how it would fit into a baselayer set for 4-season use.

Features, Fit & Finish

Sizing & Fit

Unworn and from a distance the Brynje Super Thermo looks like a pretty regular crew neck top.  It's made from 100% polypropylene, the majority of it being a mesh knit and the rest (the cuffs, hems and shoulder inlays) employs a regular 140g/sm polypropylene weave. It has no stretchy elastane in its mix; the mesh itself provides the stretch required for a close fit.  Brynje offer a wide range of sizes from XXS to XXXL and the size guide I'd read stated the Large was for 41" chest and the XL was for 42.5" chest.  I didn't want it to be overly diggy or too tight so I opted for the XL.  I'm pretty sure a size Large would have been fine, but the XL worked well and was extremely comfortable to the point of going entirely unnoticed.

The Brynje Super Thermo - A Mesh Masterpiece with a long historyThe Brynje Super Thermo looks pretty standard until you get a little closer

The Mesh

Up close, we can see the Super Thermo is made from a substantial mesh. Picking up the Super Thermo, it feels heavier than it actually is (160g for my size XL). Polypropylene has a low specific gravity and is 34% lighter than polyester and 20% lighter than nylon. Furthermore, much of this baselayer is air, so Brynje are able to allocate a significant weight of light yet strong polypropylene to structure the mesh, resulting in a robust grid scaffold over which an additional layer can create semi-permeable pockets of air.

The Brynje Super Thermo's Mesh Knit StructureThe Brynje Super Thermo features a robust mesh to create large air pockets - the key to its thermo-regulating properties.

Crew Neck

The 2023 winter kit test was not that cold, instead temperatures swung wildly from cool (-5℃) and windy to unseasonably warm (+9℃) and gale force. What surprised me was that I didn't really notice the difference that much. I never once went to unzip my baselayer to remember that it had no zip, nor reach to pull up the collar-less collar.

Due to their mesh structure, most of the Brynje mesh tops are crew necks. A good flip-top balaclava will cover the shoulders and upper chest and will function as a neck gaiter when the hood is not deployed. When getting dressed, I put on my balaclava first and put the baselayer over the top, so a collar in cold conditions isn't really that necessary.  Furthermore, the Brynje shirt seemed to do such a good job in the thermo-regulation department that even though periods of high-activity spanned a range of 14℃, I didn't need to vent at the baselayer level.  Instead I'd just adjust the softshell and leave the baselayers alone; a very good sign the baselayers are doing an excellent job.  So, as far as the Brynje Super Thermo is concerned the crew neck and lack of collar and zip was a non-issue.

The Super Thermo has a comfortable crew neckThe Brynje Super Thermo features a well finished comfortable crew neck.

The Brynje Super Thermo is a quality item and pictured above we can see the top-notch finishing that carries through each of the non-mesh elements.

Shoulder Inlays & Seams

The Super Thermo version we tested has shoulder inlays which help ensure the mesh doesn't dig into your shoulders or cause chafing when carrying a heavy pack. I had no issues in this regard; it's a sensible option for anyone carrying a multi-day load.  

The Brynje Super Thermo Shirt with shoulder inlays for carrying larger packsThe shoulder inlays (for carrying larger packs) and ultra-low profile flat-locked seams prevent chafing.

The Brynje Super Thermo comes in a short sleeve version

The seams are flat-locked, ultra low-proile and very well executed and go unnoticed.

Brynje make a short sleeve (SS) t-shirt version of the Super Thermo crew also with shoulder inlays. In retrospect I think this would be just as good if not a superior option.  Afterall, if you're wearing wrist gaiters and/or gloves, you can forego the upper forearm which is not overly prone to the feeling the cold. Of course, here we're assuming wearing a decent long sleeved, fitted baselayer over the SS version.

The "Brynje Super Thermo T-shirt with Should Inlay" also retails for around £11 less and in our view is well worth considering.

Cuffs & Hem

The cuffs are pretty standard fare and have a degree of stretch to them, but not enough to roll up beyond the forearm.  But then this is not the kind of layer that you need to be roll up the sleeves to vent; instead just roll up the sleeves of the second layer and plenty of fresh air will grace and cool your skin.

The Brynje Super Thermo's no-nonsense cuffsThe Brynje Super Thermo has pretty standard cuffs with a little stretch to them.

Below you can see a minor cost of the XL sizing (for me at least); slightly long in the arm.  But even in areas the top bunched up, it didn't create any issues.

The Brynje Super Thermo and the classic Extremities Wrist Gaiter A little bunching in the arm of the XL version.

At the base of the garment is the hem which is finished in the same way as the crew neck; a doubled-over layer with an additional central stitch securing the mesh. No issues here - all high quality stuff.

The Brynje Super Thermo's neck, cuff and hem are all finished to a high standardHigh quality finishing at the neck, cuff and hem.


As we've mentioned many times before, when an item goes unnoticed, it's a very good sign.  The 2023 winter kit test was close to ideal for testing a baselayer (though we'd have preferred lower minimum temperatures).  A third of the way through the 8 day kit test, the wind changed direction overnight, bringing warm gale force winds up from the south and the snow and ice melted away in a flash.  From scraping over icy rock in my crampons, I was now being blown over by insane winds, the temperature had jumped 14℃.

It didn't dawn on me until the end of the trip, but I'd not really noticed the change, at least not in terms of feeling warm, cold, dry or wet. The nature of the challenge and conditions had changed markedly, but under my softshell, I'd felt pretty much the same throughout the eight days.

The Brynje Super Thermo under a Megmeister Drynamo CrewWe tested the Brynje Super Thermo under our 3-season choice, the Megmeister Drynamo Crew

Over the Brynje I wore the Megmeister Drynamo LS Baselayer (pictured above). The Drynamo is a stretchy polypropylene / nylon / elastane mix and has a slightly spongy feel and with its excellent wicking properties, complements the Brynje top very well; moving moisture away from the skin to the outer layers.

One of the most noticeable benefits of the Brynje especially, but the Megmeister too, was when not being worn. The water absorption of polypropylene fibre is about 0.3% after 24 hours immersion in water, and thus its regain – the amount of water absorbed in a humid atmosphere – is virtually nil (0.05% at 65% RH, 21 °C). As such, I was able to store the "damp-feeling" Brynje in my sleeping bag overnight (every night) and along with the Drynamo give it the body-heat radiator treatment. It was so nice being able to put on a dry (or practically dry) baselayer in sub-zero temperatures. Being 100% polypropylene mesh means: 1) less fabric is touching the skin; and 2) the fabric that is touching the skin is largely dry.

In our review of the Mizuno wind top we wrote:

Getting changed into wet clothing when the temperature is below freezing is not pleasant. Getting everything packed up takes time and is not a sufficiently intense activity to generate much heat. Layering the Mizuno wind-top (that is almost too thin to hold moisture) over a merino baselayer does a number of things: 1) it allows your body to warm the damp baselayer without that warmth escaping, creating a kind of warm, moist micro-climate; 2) it shields the baselayer from getting saturated from wet outer layers; and 3) it helps block heat loss from convection. This has made a big difference in terms of comfort and reduced shivering on those all too typical UK winter mornings where yesterday's persistent deluge is followed by a deep freeze.

With the Brynje Super Thermo, this process is unnecessary. I was able to put on my balaclava, then the Brynje and Drynamo layers and wasn't instantly struck by the morning shakes. I'd just put my main insulation pieces over the top and start packing.

The Brynje costs ~£50 at full price. £50 over 8 days is £6.25. Perhaps I'm just a softy, but I'd probably pay £6.25 a day to avoid the sub-zero "wet baselayer morning" experience described above. I have to say, this was one of the times I really did notice the Brynje Super Thermo and here it gets a giant green tick in a traditionally uncomfortable box.


In Context: A Flexible 4-Season Baselayer Set

We're perhaps over-stating the "modularity" aspect, but the switch from the traditional merino-blend baselayers to a single mesh layer, does indeed provide a little more flexibility. In essence you're taking a double-layered material-blend top (designed purely for winter use) and reducing down to a single layer mesh. This allows us to pair that single next-to-skin mesh layer with one of two different types of baselayer.

A flexible mix & match approach: A 4-season base layer set

My approach is as follows:

  • Brynje Super Thermo + Megmeister Drynamo
    for winter or extremely saturated and cold environments
  • Brynje Super Thermo + Rab Sonic (LS)
    for highly saturated cool environments
  • Megmeister Drynamo
    for all-round spring and autumn use
  • Rab Sonic (LS - any variation, we're testing the "ultra" this summer)
    for summer (and for the Sonic I'd recommend sizing up as what we're after here is a loose airy fit).  Further, when it comes to Rab's ultralight Sonic, the sleeves on the LS version can be rolled up above the bicep and so the long sleeve version does just as good a venting job than the short sleeve version. 

Any Negatives?

At present we can't think of any. If you accept the case laid out above, the only issue is which one to go for.  We've been so impressed by the Brynje Super Thermo we're going to pick up a short sleeve versions for next winter's kit test. My guess is that the short sleeve version (see product images below) may well be perfectly adequate (and it's £11 cheaper). 

In terms of durability, it's too early to say, but from our research and reading customer reviews we've not seen any red flags and there were no signs of wear and tear post kit test. We'll update this review if there's anything to report, but from a close inspection of how it's put together, the quality of the materials and the fact that Brynje have been turning these out for decades - it's not something we're overly concerned about.


Conclusion & Rating

The purpose of a baselayer is to move moisture and excess heat away from the skin and achieve a thermal balance that doesn't fluctuate too much throughout the day as conditions and activity levels vary.  This is precisely what the Brynje Super Thermo accomplishes as the next-to-skin layer in a two-layer set for sub-zero conditions.

In terms of surface area, much of the Brynje Super Thermo is made of air, the rest is made from two different weaves of polypropylene: 1) a robust polypropylene mesh, and 2) a denser weave for the shoulder inlays, hems and cuffs. Polypropylene is profoundly hydrophobic (its regain – the amount of water absorbed in a humid atmosphere – is virtually nil) and this combination of warm air pockets in a hydrophobic mesh promotes moisture transport and keeps the wearer feeling dry.

Furthermore, because the top is basically a hydrophobic mesh it dries very rapidly and so it affords one the luxury of being able to put on a dry top in sub-zero conditions avoiding the unpleasant experience of putting on wet clothes when it's freezing.

Brynje have been perfecting the mesh baselayer for around 100 years and you can see why the concept hasn't changed that much. It clearly works and with the ever-rocketing prices of the merino-blend (oil+sheep) competition, the case for a purely synthetic approach gets stronger every day (we'll leave the "net zero" fanatics to weigh and measure the sins of sheep farts versus petroleum derivatives).

The shoulder inlay version is strongly recommended for anyone carrying multi-day loads as these prevent chafing and possible discomfort from pack straps.

The Brynje Super Thermo is a high quality, superbly finished, mesh masterpiece with an enduring history and if the old prototypes were good enough for Hillary and Tenzing, the modern version is probably good enough for us Scramblers.  The Brynje Super Thermo is our top pick in the Cold Weather Baselayer category. 


Product Images


Rating (out of 10)

RRP Value *

* The value score is derived from two factors:
1) Competitive Market Price (CMP). This represents our judgement of a competitive online price point if we were to stock the item. e.g. if we feel we would need to sell an item at 40% off (i.e. 60% of its full RRP) to be competitive, then our CMP score will be 6/10.
2) Customer Value Price (CVP). We then make an honest appraisal of the maximum price we would be willing to pay for the item (and we're mean). So if we'd pay 80% of its RRP our CVP score would be 8/10.
We then average the two scores to get our final value score, which in our example would be 7/10.


Postscript: Why Polypropylene?

What's so special about Polypropylene? Well, quite a bit ...

From the standpoint of a lightweight baselayer it's hard to envisage a more appropriate material:

  • Lightweight: Because of its low specific gravity, polypropylene yields the greatest volume of fibre for a given weight. Polypropylene is the lightest of all fibres and is lighter than water. It is 34% lighter than polyester and 20% lighter than nylon.
  • Hydrophobic, thus quick to dry: The water absorption of polypropylene fibre is about 0.3% after 24 hours immersion in water, and thus its regain – the amount of water absorbed in a humid atmosphere – is virtually nil (0.05% at 65% RH, 21 °C.). Being hydrophobic it will not absorb water into the fibre, instead water “wicks” away from the skin and through the fabric to the face for quick evaporation.
  • Cold weather performance: Lowest thermal conductivity of any natural or synthetic fibre (6.0 compared to 7.3 for wool, 11.2 for viscose and 17.5 for cotton). Polypropylene fibres retain more heat for a longer period of time providing outstanding insulation and combined with its hydrophobic qualities keeps the wearer dry as well as warm. Polypropylene is warmer than wool, remains flexible at temperatures in the region of -55°C and recovers well from bending.
  • Microbially inert: Like other synthetic fibres – nylon, acrylic and polyester – polypropylene fibres are not attacked by bacteria or micro-organisms; they are also moth-proof and rot-proof and are inherently resistant to the growth of mildew and mold.
  • Abrasion resistant: The abrasion resistance of polypropylene approaches that of nylon and remains high even when wet.


Last Updated: 08/08/23

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