How do you stay warm when the air is cold?

Let’s start with the basics. Every winter layering system begins with the 3-layer concept – base, insulation, and shell.  (There are some new technologies that blur these lines, but we’ll get to that a bit later.)  The base layer sits tight to your skin and serves the dual purpose of feeling nice and wicking sweat.  Your insulating mid-layer carries most of the heat-keeping duties.  And, the outer shell is tasked with keeping the elements out.  Three layers seems to be the perfect amount for both versatility and temperature control.  You can always pack the insulation away during high effort and put it back on when things calm down.  More layers and things get bulky and cumbersome.  Fewer layers (or sometimes, combining layers) reduces their effectiveness and versatility.

We hinted at it above, but there are some situations and some technologies that blur the lines between base, mid, and outer layers.  And, there are always exceptions to the rules.  What follows are general guidelines and basic advice for putting together a winter layering system.  If you’re headed to the Arctic or live on a tropical island, your mileage may vary!

Base Layers

The ideal base layer has a soft hand for comfort and some way to move your sweat away from your body.  It should fit close to the skin to prevent bunching, but it shouldn’t be so tight that it squeezes things.  We recommend merino, merino-blend, and synthetic base layers.  Please, do not ever wear cotton.  If you still have those waffle-knit long johns, keep them for cozy nights in front of the fireplace, but never wear them out while being active in the cold.  Cotton holds moisture and dries slowly, which sucks heat out of your body.  That’s bad!

TREW Gear NuYarn

Merino seems to be a good fiber for those who tend to run cold and those that need odor resistance (though that is starting to change).  Merino can come in various weights, but an ideal base layer is around 200wt.  It naturally resists odors, so you won’t be stinky on long backcountry trips.  Or, on shorter, but sweaty, trips, you can hang out at apres without driving the next table away.  Pure merino won’t dry as quickly as a merino blend or full synthetic, but it is warm.  We like pure merino for base layer bottoms because it’s harder to find a good mid-layer for your legs.  There are some great options from Ibex and Smartwool.

Some of our favorite base layers are merino-blends.  These take various forms.  TREW Gear‘s NuYarn and Arc’teryx’s Satoro AR wrap merino fibers around a synthetic core.  Other companies utilize Polartec’s Powerwool, which puts the merino against your skin and a synthetic layer on the exterior face of the fabric.  The idea is to get a best-of-both-worlds combination of merino’s comfort and insulating properties with the synthetic’s ability to pull moisture out and spread it over a large surface area to evaporate.

If you’re an especially sweaty person, vegan, or if you’re allergic to wool, synthetics have you covered.  Synthetics have a preternatural ability to wick sweat and dry quickly.  And, although they’ve earned their reputation for being stinky (poly-pew, anyone?), new tech allows them to match and sometimes exceed merino’s anti-stink qualities.  Patagonia, for example, is one of a few companies infusing their Capilene base layers with Polygiene, which uses silver particles to pretty much stab stinky bacteria to death.

Speaking of Patagonia, we’d be remiss in not mentioning their stellar Merino Air pieces.  Despite being only 190wt fabric, Merino Air is woven to create air spaces inside, keeping you exceptionally warm for the weight while maintaining breathability.  It’s also seam-free so you won’t chafe during repetitive movements like skinning up the hill.  With a 51/49% blend of Merino and recycled polyester, it hits the mark for natural odor resistance and wicking ability.


Things get more complicated here, so we’ll try to simplify as much as we can.  With all mid-layers, pick the layer that will provide the right amount of insulation for your activities.  If you run warm and will be charging hard, don’t put on a heavy mid-layer.  A layer with 40g synthetic or a down sweater will do the trick.  Likewise, if you run cold or don’t plan to be moving around much, a heavier layer will be essential for staying warm.


First, for most active pursuits, take down off your list.  Down still has unmatched warmth to weight ratios and lofts up more than any synthetic.  But, even with the advent of so-called water-resistant down, feathers still wet out and dry slowly.  With the interesting advances in air-permeable synthetic insulation, there are a ton of choices out there that will excel at retaining heat, expelling moisture, and doing that all day long.

Synthetic insulation is measured in grams per square meter.  The higher the number the warmer the insulation.  So, 100g is warmer than 60g is warmer than 40g.  Most jackets come with 60g insulation; 40g and 100g seem to be for more specialized items.

Big Agnes Dunkley Belay Parka Jacket Review

In choosing a mid-layer, your focus should be on the function of the insulation and the fit of the piece.  With that in mind, there are a few types of insulation you should look at: 1) Polartec Alpha; 2) Patagonia FullRange; and 3) Arc’teryx Coreloft.  Of those three, FullRange is currently the top dog.  It offers 40+CFM of air permeability, which is just about as much breathability as you can have without having too much.  Polartec’s Alpha appears, to us at least, to be a very loosely knit fleece layer held captive between face fabrics.  The loose knit adds breathability.  Where Alpha loses out, though, is on packability – it doesn’t compress as well.  Though we can’t find any definitive numbers, Patagonia claims that FullRange is twice as breathable as “its competitor.”  Our experience is that companies that use Alpha tend to pair it with fabrics that inhibit its breathability, which is unfortunate.  Lastly, Arc’teryx is jumping in the game of air-permeable mid-layers with jackets like the Proton LT and the updated Atom LT.  They aren’t as flowy as the Patagonia, but still breath.  We think their Coreloft insulation is probably capable of more breathing, but Arc’teryx has, so far, chosen to put it inside less breathable face fabrics.

Primaloft, the grand-daddy of synthetic insulation, has also updated their lineup of options – Gold is the warmest, but you sacrifice some breathability/mobility, where Silver is a good mix of warmth and breathability. Anywhere that you see “Eco”, that product is made up of 55% recycled materials.  You’ll find Primaloft in jackets from brands like La Sportiva, SalomonNorrona, and The North Face (yup, their Thermoball insulation is from Primaloft!).

Why all this focus on breathing insulation?  For a simple reason – if you wick all that sweat away from your skin, but trap it in your mid-layer, you end up with a wet, less effective mid-layer.  That water has to go!  So, the more your mid-layer breathes, the less moisture will get trapped.

Secondary considerations for mid-layers:  Weight – you don’t want to be carrying a polyester anvil up the mountain.  Compressability – when the day heats up and you throw the mid-layer in your pack, it shouldn’t be the only thing that fits.  Fit – if the jacket doesn’t fit, you’re gonna quit.  Different brands will fit differently, so find the one that best suits your body type.

Patagonia does not license its FullRange insulation to anyone else.  So, if you want the most breathable insulation, you only have one choice.  Polartec Alpha is available from multiple brands in multiple weights.  Outdoor Research, Rab, Mammut, and Marmot all offer jackets with Alpha.  Coreloft is only available in Arc’teryx products.


For maximum warmth to weight ratios in situations where moisture isn’t as much of an issue, down is still the way to go.  There are three types of down jackets we want to introduce you to: the ultralight, the standard, and the extreme.  But, before we get into that, let’s talk about fill power.

The best way to explain fill power is that it’s the maximum amount of space an ounce of down will take up in ideal conditions.  So, for example, an ounce of 600-fill down will take up 600 cubic inches.  Why is fill power important?  Because all insulation, whether down or synthetic, works by separating you from the cold with air.  The more air you put between yourself and the cold, the warmer you’ll be.  And, the higher the fill power, the fewer feathers you need to create that airspace.  So, 850-fill down will be warmer than 600-fill at equal weight and will weigh less for equal warmth.

Let’s start with the ultralight.  Ultralight down jackets – sometimes called down sweaters – use the lightest possible face fabric and high quality down to create maximum warmth at minimal weight.  On the extreme end, Montbell’s Plasma uses 7 denier fabric 1000-fill down.  That’s almost too light!  More standard jackets use 15-denier fabrics.  A quintessential example – Patagonia’s Ultralight Down Hoody packs 800-fill down into 15-denier Pertex Quantum.  Ultralight down jackets aren’t going to keep you toasty if you’re standing still in sub-freezing temps, but to ward off chilly weather, or if you plan on moving (but not sweating much) in cold temps, they’re a great option.

Mountain hardwear Stretchdown RS Holiday winter 2016 gift guide

Your standard down jacket can be anything from 15-denier to 40-denier fabric and will use 600- to 850-fill down.  Our current favorite comes from Mountain Hardwear in the form of their Stretchdown RS hoody.  It uses 15-denier fabric on the outside and a stretchy, knit, interior fabric with 750-fill, waterproof down in between.  It’s still light weight, weighing in under a pound, but the Stretchdown RS and other standard down jackets don’t make as many sacrifices to save weight.  They’ll keep you warm in situations where an ultralight jacket may not.  The Stretchdown RS is on the lighter end of this category.  Other, more robust examples include the Patagonia Down Sweater Hoody in the middle and the RAB Neutrino Endurance on the heavier, warmer side.

Finally, for those extreme circumstances, there’s the extreme down jacket.  If you need one of these, we probably haven’t told you anything you don’t already know.  Extreme down jackets use heavier, sometimes waterproof, fabrics to prevent failure and stuff more than a pound of down inside.  Jackets like the Mountain Hardwear Absolute Zero and The North Face Himalayan Parka are two examples of jackets most of us will never need.  But, for those who venture into extremely high altitude or high/low latitude, an extreme down jacket is absolutely essential.

New, waterproof down will keep your jacket lofty longer in wet situations, but no down is truly waterproof.  And, when it does eventually get soaked, it still takes a long time to dry.  The waterproof treatments are getting better, though, so we hope down will truly be waterproof someday soon.  Best practice is to try to keep your down dry in the first place, if you can.

Responsible Down

We think it’s important to know that the down stuffed in your jacket was sourced responsibly.  That means no live-plucking, no force feeding, and no other forms of animal mistreatment.  Many brands have signed on to the Responsible Down Standard.  Developed by The North Face and given to non-profit Textile Exchange, RDS attempts to ensure that the birds that provide certified down are treated humanely.  Patagonia has their own standard, tracing the birds that provide it from egg to slaughter.  Differences between RDS and Patagonia’s standard:

  • RDS permits a blend of certified and un-certified down in products that can be certified
  • RDS only reaches up to breeding farms; Patagonia’s standard examines parent farms as well, where the eggs are laid.
  • RDS allows parallel production – farms can force feed and live pluck right next to their RDS birds.  Patagonia does not permit this.

RDS is definitely a great step forward.  Patagonia goes multiple steps beyond.  Please make sure that the company making your jacket has signed on to RDS at the very least.  Every link we’ve provided is to a company that has signed on to RDS (except that Patagonia has its own, higher standard).  We mention the Montbell Plasma, above, but can’t confirm that Montbell uses ethical sourcing for its down.


At this stage in the layering system, we may diverge a bit from the conventional wisdom.  For the most part, we think a shell should stay in your pack until the moisture falling from the sky forces you to wear it.  That’s because even the most breathable, waterproof shell is still going to be the least breathable layer you’re wearing.  We’ll avoid getting into a whole bunch of technical jargon about millimeters and PSI and g/sq m./day and humidity gradients.  Suffice to say that despite all the claims out there, there is no waterproof, breathable membrane that will let all your sweat out.  Still, there are some that are better than others and everyone seems to be improving their technology.

Stio Snotel Jacket

For winter layering, we recommend picking a 3-layer shell, as opposed to a 2.5 layer shell.  The difference is in the durability.  A 2.5 layer shell simply won’t stand up to abrasion and other forms of jacket torture like a 3-layer shell will.  Try to find a fabric that’s at least 40-denier.  A higher denier fabric will be heavier, but will be more durable.

You’ll have to pick your membrane.  Gore used to be the only game in town.  While they’ve upped their game recently to catch up with competitors, we think they’re still behind.  eVent and Neoshell leapfrogged Gore, in a sense, by creating membranes with a bit of air permeability (there’s that term again).  While eVent and Neoshell aren’t remotely as breathable as the mid-layers above, they do allow about 1% of the air to pass through the jacket.  Also, Gore’s patent ran out in 1997, which allowed other companies to use their original PTFe membrane technology to make their own shells.  Recently, other manufacturers like Outdoor Research have been entering the market with their own, air permeable membranes, broadening the selection even more!  And, let’s not forget some of the lesser-known fabric companies like Toray, who produce Dermazix NX which is both air permeable and stretchy.

Check that the hood is compatible with your helmet and adjustable enough to wear without.  Jackets may list a helmet compatible hood, but that can mean snowsport helmets or climbing helmets.  Climbing helmets are much smaller.  You may buy a jacket with a “helmet compatible” hood only to find that it doesn’t fit over your snowsport helmet.

For active winter use, choose a shell with an air permeable membrane.  You get the benefit of both moisture diffusion – where moisture moves through the membrane from the wetter side to the dryer side – and from convection – air moving into and out of the shell and taking moisture with it.   Mountain Hardwear, Outdoor Research, Westcomb, and others produce highly technical mountain shells with air permeable membranes.  If you’re more ski/snowboard focused, companies like Stio and Strafe have you covered.  It feels strange to suggest, but for truly active winter activities, pick a membrane other than Goretex.  It just isn’t as breathable as other options.  Oddly, one of our favorite companies, Arc’teryx, has so far refused to use an air permeable membrane in their jackets.

Combining Layers

There are plenty of companies out there that make combination layers.  Things like insulated shells, fleece base layers, etc.  For the most part, we suggest skipping these.

When it comes to base layers, you don’t want to wear something thick enough that moisture can’t move all the way through it and on to the next layer.  Fleece-like base layers that have significant thickness do exactly that.  You end up trapping your sweat against your skin more than you would if you had a thin base layer.  Bad!

Likewise, insulated shells generally don’t allow the flexibility to strip and don layers as needed for climate control.  An insulated shell eliminates the possibility of wearing the shell alone over your base layer, which we think is essential on stormy, uphill treks.  With all that said, there may be an exception to this rule – the Patagonia Nano Storm jacket.  We’re still in the middle of testing, but the Nano Storm may be breathable enough that it can work as a normal shell even though it has insulation.  We’ll see!

There are also specific situations where an insulated shell may make more sense than multiple layers.  In that case, jackets like Columbia’s Outdry EX Gold Down hoody may work.  But, generally, stick with the three layer system.

Other Layers

In certain situations, you may need to add other layers to your three-layer system.  We can’t possible cover all of those possibilities here.  Some examples may include: a giant, puffy belay parka for moments of rest after high activity where it’s not wise to remove the layers you already have on; a windproof fleece vest for highly aerobic activities on a bone-chilling, but sunny day; a vapor barrier base layer in exceptionally cold, extreme climates.  If you need one of these layers, this primer probably wasn’t new information to you anyway!

What about Softshells?

Softshells are great in the right circumstances, but the term is pretty broad.  You can find jackets with hard-face fleece that will block wind but not much else.  On the other end of the spectrum, there are softshells that have a membrane layer, essentially giving you a stretchy shell with a soft inner face.  These pieces can replace a mid-layer or shell, but may not function as well.  A hard-face fleece softshell won’t be as warm for the weight as a synthetic or down puffy.  It also won’t compress as much.  Softshells with membranes are nice, but weigh more than an equivalent hardshell and, if you have layered correctly underneath, they won’t add any functional warmth.  Softshells come into their own when you need wind protection and some warmth during cold, dry activity.  Ice climbing in good weather is perfect for softshells (with a belay parka for belaying).

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