A layering system is a way of dressing where every garment does one job: the base layer moves moisture off your skin, the mid layer traps heat, the shell blocks wind and water, and an insulated parka covers the times you are not moving. You build the kit around your activity and the weather, not around a number on a thermometer: fewer layers while moving, more when static.
Why people freeze in expensive clothing
The usual story: someone buys a warm jacket, wears it on a move, sweats through in twenty minutes, opens it up, and then shakes with cold an hour into a static position. The clothing is expensive and the result is worse than for the person wearing three thin pieces.
The reason is physical. Water conducts heat roughly 24 to 25 times faster than still air. The moment the layer against your skin gets wet with sweat, it stops insulating and starts pulling heat out of you. In winter your enemy is rarely the frost itself — it is your own sweat with nowhere to go.
Where the layering system comes from
The modern approach grew out of the US Army ECWCS (Extended Cold Weather Clothing System). Its third generation is seven levels and twelve items weighing about 5.8 kg in total, developed by the Natick Soldier Center. The move from a four-layer scheme to seven levels happened for exactly the reason above: one thick jacket only works inside a narrow window, while a modular kit covers both movement and stillness.
An important clarification most articles skip: the official temperatures in the ECWCS manual are tied to combinations of levels in a specific activity, not to individual garments. Statements like «level one works from +10 to +20» are someone's interpretation, not a document.
How the army actually assigns temperatures
Below is the logic of the official manual. Its value is not in the level names but in the principle: the same kit behaves differently when you move and when you sit still.
| Mode | Conditions | Temperature | Kit logic |
|---|---|---|---|
| Active | Wet weather | around +4 °C | Base plus wind shell or softshell, no insulation |
| Active | Cold | −18 to −1 °C | Base, mid layer, softshell |
| Active | Extreme cold | −32 to −18 °C | Base, mid layer, fleece, softshell |
| Static | Cold and wet | −1 to +7 °C | Base, fleece, hard shell |
| Static | Cold | −18 to −1 °C | Mid layer, softshell, insulated parka |
| Static | Extreme cold | −46 to −18 °C | Every layer plus the insulated parka |
Notice that the insulated parka appears only in static configurations. It is absent from every official active combination — which is the answer for anyone who wears a winter jacket all day long.
How the system maps onto the UATAC range
We do not copy the army nomenclature, because a Ukrainian winter and real tasks differ from an Alaskan training ground. The logic of the levels is kept, and every category in the catalogue covers its own function.
| Function | What it is at UATAC | Job of the layer |
|---|---|---|
| Base (skin) | Base layers: cotton briefs, merino trekking socks | Comfort, hygiene, moisture control on the feet |
| Base (thermal) | Micro-fleece thermal shirt | Moisture transport and thin insulation under armour |
| Top under armour | Combat shirts Gen 5.6 and Gen 5.7 | Torso cooling, abrasion resistance on sleeves, elbow protection |
| Bottom | Assault pants Gen 5.6 / 5.7 | Durability, knee protection, venting |
| Mid | Fleece Gen 3: micro-fleece, Ultrasoft Termo | Heat retention and day-to-day regulation |
| Shell | Demi-season jackets: ripstop and membrane | Wind, rain, wet snow |
| Insulated shell | Winter jackets with Climashield APEX 100 and 136 | Static work in hard frost |
Layer one: what touches your skin
This is the cheapest part of the kit and the one that decides the most. If the base layer does not move moisture, the rest of the system runs empty: water stays against your body, insulation collapses, and the most expensive jacket cannot save it.
Here is a piece of honesty you rarely get from a brand. Our catalogue includes cotton briefs, and that is a deliberate choice for everyday wear, rear-area duty and warm weather, where comfort and hygiene matter more. But under body armour in the cold and on long movements, cotton next to the skin works against you: it soaks up moisture, dries slowly and chills you the moment you stop. For those conditions take a synthetic or micro-fleece thermal layer.
The UATAC micro-fleece thermal shirt covers exactly that job: thin, moves moisture outward, adds a little insulation without adding bulk under a plate carrier.
Feet deserve a separate note. UATAC merino wool trekking socks are the case where a natural fibre earns its place: merino still insulates when damp, holds odour back longer and chafes less on long movements. Wet socks are one of the fastest routes to hypothermia, so a spare pair is not optional.
The combat shirt: a layer the army scheme never had
The classic layering system was born before plate carriers were worn all day, so formally there is no combat shirt in it. In practice it became a layer of its own, because it solves a problem mountaineers never had: the carrier covers your torso with a solid, impermeable panel and blocks evaporation.
The numbers are blunt. The torso zones covered by armour amount to roughly a quarter of body surface, and evaporative resistance in that area rises close to threefold. In plain terms, under the plate your clothing almost stops breathing — and no amount of jacket venting compensates for that.
That is why the UATAC Gen 5.7 combat shirt uses a NyCoLy knit torso with NILIT BREEZE nylon, which lowers body temperature under load and moves moisture out, while the sleeves are Ripstop because they rub against ground and gear. There is mesh under the arms, CORDURA 500d on the elbows, and EVA elbow pads in the box.
Pants are part of the system too
The lower half gets forgotten, even though legs give away a lot of heat when you sit on cold ground. UATAC assault pants Gen 5.6 and 5.7 are built on 65/35 Ripstop with a Teflon finish, a double-layer seat, CORDURA 500d knee reinforcement and venting zones.
In hard frost a thermal layer goes underneath; in shoulder seasons they work on their own. Do not buy them skin-tight: if a base layer will not fit under the pants, the winter system simply will not assemble.
The mid layer: fleece is what makes the system adjustable
Fleece is the piece you take off and put back on several times a day. It is what makes the kit controllable: base layer and pants stay on, the shell follows the weather, and fleece fine-tunes warmth against activity.
In the army system the fleece level is specified at roughly 1.3 Clo of insulation at about 6.4 ounces per square yard. The useful takeaway is not the number but the principle: a mid layer should insulate through structure, not thickness.
The UATAC Gen 3 line gives you two working options. The micro-fleece is thin, adds almost no bulk, sits well under a combat shirt and plate carrier, and suits shoulder seasons and active movement. Ultrasoft Termo is denser, made for cold and static work, and functions under a jacket or as an outer piece on a dry day.
A practical rule: if you are choosing between one dense fleece and two thin pieces, take the two. The air gap between them is exactly what holds heat.
The shell: wind and water
A shell does not warm you. Its job is to stop wind from stripping the warm air out of your clothing and to keep water away from the inner layers. The choice is between treated ripstop and a membrane.
| Type | What it gives | When to choose it | Limitation |
|---|---|---|---|
| Treated ripstop | Wind protection, sheds spray and dry snow | Dry frost, active tasks | Wets out in prolonged rain |
| Membrane 10,000/10,000 | Holds sustained precipitation, vents vapour | Wet winter, wet snow | Needs the right base layer |
| Membrane 20,000/10,000 | Maximum water protection | Long exposure, gear straps | Overkill in dry climates |
The numbers read simply: the first is hydrostatic head in millimetres of water column before the fabric leaks, the second is breathability in grams of vapour per square metre per 24 hours. Pack and plate-carrier straps press locally on the fabric, so a higher rating is justified when you work under gear.
One caveat decides everything: a membrane only works with a proper base layer. A cotton T-shirt underneath cancels it out, because moisture never reaches the membrane — it stays on you.
The winter jacket: a layer for standing still
In the army system the insulated parka stands apart and appears only in static configurations. Its insulation is specified at about six ounces per square yard, roughly two hundred grams per square metre — that is survival equipment for cold without movement, not an everyday jacket.
UATAC winter jackets are built on Climashield APEX in two weights. 100 gsm for an active winter with movement. 136 gsm for positions, vehicles and guard duty. Some models are membrane versions, and in a wet winter that often matters more than extra grams of fill.
Why APEX rather than down or cheap wadding: it is laid as a continuous sheet, does not migrate inside the baffles and needs far less quilting — and every through-stitch is a cold bridge. When damp, synthetic keeps insulating, while down clumps and stops working.
Why the layers complement rather than duplicate each other
Each layer owns a different piece of physics. The base deals with moisture at the skin. The mid holds air. The shell stops wind and water. The insulated layer compensates for the absence of movement.
Remove one and the failure is predictable: without a base you are wet, without fleece you freeze the moment you stop, without a shell the wind takes your heat, and without an insulated jacket static work in frost becomes dangerous. Spread the budget across the system instead of putting it all into one expensive jacket.
| Remove this | What happens |
|---|---|
| Base layer | Moisture stays against the body and insulation collapses |
| Fleece | Nothing left to regulate heat between movement and rest |
| Shell | Wind strips the warmed air out of the kit |
| Winter jacket | Static work in frost becomes dangerous |
A wet winter is harder on clothing than a dry freeze
Average January temperatures in Ukraine run from about minus seven in the north-east to plus two to four in the south, and the weather is shaped by humid Atlantic air with thaws, snowfalls and westerly winds. That means constant crossings of the freezing point and high humidity.
For clothing this is a harder regime than stable frost. In dry cold, sweat partly crystallises and can be brushed off the fabric. Around zero with high humidity it stays liquid, accumulates in the layers, and the physics we started with takes over: wet fabric pulls heat away many times faster than dry.
The practical conclusion for most of Ukraine, and for any maritime winter climate: water protection and moisture transport matter more than maximum insulation weight. A membrane jacket with APEX 100 over a working base layer delivers more real warmth in a wet winter than a thick jacket over a cotton T-shirt.
Mistakes that cost you
- Wearing everything at once. You start warm, get soaked in ten minutes and freeze at the first halt. Step out slightly cold and warm up through movement.
- Cotton against the skin in the cold. It absorbs moisture, dries slowly and chills you in any draught.
- Layers that are too tight. They compress the air gap and restrict circulation — cold hands and feet in an otherwise warm kit.
- Wearing the winter jacket constantly. In official combinations the insulated parka appears only in static work.
- Ignoring head, neck and feet. A balaclava, a neck gaiter and spare socks often beat another torso layer.
- Buying every layer in a snug size. The system will not assemble: no thermal under the pants, no fleece under the jacket.
What a layering system does not do
It does not produce heat. Your body does; the clothing only manages the losses. If you have not eaten, drunk or moved, no combination of layers will keep hypothermia away.
It is also not protection — neither ballistic nor flame. And it does not hide you from thermal imaging: a well-insulated kit actually increases the contrast between covered body and exposed skin.
How to build the kit, step by step
- Define your mode: mostly movement or mostly static. That is the main variable.
- Start with the base: micro-fleece thermal shirt and merino socks, with a spare pair.
- Add the top under armour: a combat shirt in the same camouflage as your pants.
- Take assault pants with knee pads, sized with room for a base layer.
- Add fleece: micro-fleece for movement, Ultrasoft Termo for cold.
- Choose the shell by climate: ripstop for dry frost, membrane for a wet winter.
- For static work in frost, add a winter jacket with APEX 100 or 136.
- Close the gaps: headwear, neck protection, spare base layer in a dry bag.
Frequently asked questions
What is a clothing layering system?
A principle where each garment does one job: the base layer moves moisture off the skin, the mid layer traps heat, the shell blocks wind and water, and an insulated jacket compensates for the lack of movement.
How many layers do I need in winter?
It depends on activity. On the move you usually run base, mid and shell. Static work adds the insulated jacket. Wearing everything at once while moving is the classic mistake.
Why is cotton a bad idea in the cold?
Cotton absorbs moisture and dries slowly, and water conducts heat roughly 24 to 25 times faster than still air. Wet cotton against the skin acts as a heat sink.
Can one warm jacket replace a layering system?
No. A single thick jacket works only in a narrow window: too hot on the move, not enough when static in frost. Modularity is the whole point.
Which fleece should I choose, thin or dense?
Micro-fleece for active movement and shoulder seasons, since it adds less bulk under armour. Ultrasoft Termo for cold and static tasks.
What matters more, insulation or a membrane?
In a wet winter, usually the membrane: wind and water take more heat than the difference of a few dozen grams of fill.
How do layers work under body armour?
Armour blocks evaporation across a large part of the torso, so you need thin moisture-moving layers underneath and should look for ventilation outside the plate area: sleeves, back below the panel, neck.
Where should I start on a limited budget?
With the base layer and pants. They are what you wear every day and what affects comfort the most. The jacket can come later.
Author: Serhii Vynnyk, founder and CEO of UATAC. Updated: 14 September 2026. Temperature combinations follow the logic of the US Army ECWCS Gen III manual; Clo values and insulation weights come from the system specifications. Where a figure is an interpretation rather than a document, it is stated in the text.