The warmest option in the range is a winter jacket with Climashield® APEX at 136 gsm, especially in the membrane version. It is built for static work in frost: fighting positions, observation posts, vehicles, guard duty. For active movement 100 gsm is the more practical choice.
Why the warmest jacket is not always the right one
The classic mistake is buying maximum insulation «so I definitely will not freeze». A week later it turns out the jacket is too hot on the move. You sweat, the base layer soaks through, and at the first halt wet clothing pulls heat away faster than the jacket can put it back. The person who bought the warmest thing is the one who ends up cold.
Heat in the field is produced by your body. The jacket only retains it and blocks wind and water. So choose for your mode of work, not for the maximum number.
How to choose by mode
| Mode | What to take | Why |
|---|---|---|
| Static: position, guard duty, vehicle | APEX 136 gsm, preferably with a membrane | Heat has to be retained, not generated |
| Mixed: movement with halts | APEX 100 gsm plus a fleece | Layers adjust, a single fill does not |
| Active movement | APEX 100 gsm | Less bulk, less sweat |
| Wet winter, wet snow | Membrane version | Wind and water take more heat than missing grams of fill |
A membrane often matters more than grams
In a damp winter, wind and wet snow strip heat faster than a slightly lower insulation weight loses it. A membrane jacket with APEX 136 feels warmer in those conditions than a non-membrane one at the same weight.
Warmth is a system, not a single item
The jacket works together with a base layer and a fleece. The air trapped between layers is what holds heat, while the base layer moves moisture out so it does not accumulate inside. One thick layer always loses to three correct ones.
Common mistakes
- Buying maximum insulation weight for an active mode of work.
- Relying on the jacket alone and skipping the base layer and fleece.
- Wearing the jacket constantly instead of taking it off while moving.
- Storing it compressed, which costs the insulation its loft.
- Drying it next to a stove after a task.
What a jacket will not do
It does not generate heat and does not compensate for a lack of food, water or movement in the cold. It also does not hide you from thermal imaging — a well-insulated garment actually increases the contrast between a covered body and exposed skin.
Selection checklist
- Define the mode: static or movement.
- Assess the climate: dry frost or wet winter.
- Choose the weight: 136 gsm for static, 100 gsm for movement.
- Decide on a membrane based on regional humidity.
- Size with room for a fleece.
- Check that the jacket has venting.
Frequently asked questions
Which UATAC jacket is the warmest?
A winter jacket with Climashield® APEX at 136 gsm, primarily in the membrane version.
Should I take 136 gsm if I move a lot?
No, 100 gsm plus a fleece is better. Excess insulation in movement leads to sweating, and damp clothing chills you at a halt.
What is warmer, more insulation or a membrane?
In a wet winter a membrane often delivers more real warmth, because it blocks wind and water — the main channels of heat loss.
Can a winter jacket be worn over body armour?
Yes, that is a standard use case. You need a roomy cut, side venting and waist adjustment.
How should I store the jacket in summer?
Loosely hung rather than compressed in a stuff sack, since sustained compression reduces the loft of the insulation.
Author: Serhii Vynnyk, founder and CEO of UATAC. Updated: 16 September 2026.