2L, 3L, and What 20K/20K Actually Means

Outerwear is sold with numbers on it — 2L, 3L, 20K/20K — and almost nobody explains what they mean. They are not marketing. They describe real construction decisions that change what a jacket can do, and once you know how to read them you can tell in about four seconds whether a jacket suits what you actually do.

What a waterproof fabric is

Every waterproof-breathable garment is built around a membrane: a thin film with pores large enough to let water vapour molecules escape and small enough to stop liquid water getting in. That membrane is fragile. On its own it would not survive a season, so it always gets bonded to a face fabric on the outside, which takes the abrasion.

What you do about the inside is what separates 2-layer from 3-layer.

2-layer

Face fabric and membrane bonded together — that is the two layers — with a separate liner hanging loose behind them.

Because that liner is separate, there is room between it and the membrane. That space is where insulation goes. This is why almost every insulated ski jacket in the world is 2L: it is the construction that lets a manufacturer build warmth into the garment itself.

MURMUR™ is 2L, insulated and waterproof. One jacket, one decision, warm on a chairlift. That is the trade: you get a complete resort jacket out of the box, and you give up the ability to remove the insulation when you start working hard.

3-layer

Face fabric, membrane and a knit or tricot backer, all bonded into a single piece of material. No loose liner. No insulation.

What you get is a fabric that is more durable, more breathable and more packable, because there is no separate liner to trap air, hold moisture or wear against the membrane from the inside. What you give up is built-in warmth — a 3L shell on its own, in the cold, with nothing under it, is not warm.

That is the point. TALON™ is 3L and carries no insulation because the warmth belongs one layer down, on a HACKLE™ or COVERT™ midlayer you can take off when you start climbing. It is the more adaptable system and the more expensive one, and it is the right answer if your day involves going uphill under your own power.

So which one

The question is not which is better. It is whether your output changes during the day.

Resort skiing. Chairlift up, ski down, output relatively constant and mostly low. You are not going to be stripping layers on a lift. 2L insulated — MURMUR™ — is less faff and warmer for the money.

Touring, freeride, anything with a climb in it. Output swings from very high on the way up to nothing on the way down. You need to be able to remove warmth without removing weather protection. 3L shell plus a separate midlayer — TALON™ over HACKLE™.

Both, on a budget. Buy the 3L shell. A shell plus midlayer can imitate an insulated jacket. An insulated jacket cannot imitate a shell.

Reading 20K/20K

Two separate measurements, always written waterproofing first.

The first number is the hydrostatic head, in millimetres. Seal a tube to the fabric and fill it with water: 20,000 mm means a twenty-metre column can sit there before it forces its way through. Nobody stands under a twenty-metre column of water. The number matters because pressure is what beats a fabric, and pressure comes from you — a pack strap, a knee in wet snow, sitting on a wet chairlift. Rain alone needs about 5,000 mm. Sitting down in slush needs far more.

The second number is breathability, in grams of water vapour passing through a square metre of fabric in 24 hours. 20,000 g/m²/24h means the fabric can move a serious amount of sweat. This is the number that decides whether you arrive at the top wet from the inside.

Rough guide: 5K/5K is a rain jacket for walking to the station. 10K/10K is fine for resort days in reliable weather. 20K/20K is the point at which the shell stops being the limiting factor — where, if you get wet, it is because of what you did, not what you wore.

The part nobody tells you

Breathability numbers are measured on clean fabric in a lab. In the real world the thing that stops a shell breathing is not the membrane — it is the face fabric on the outside getting saturated.

New face fabric has a DWR finish that makes water bead and roll off. As the fabric picks up dirt, sweat and body oils, that finish stops working. Water spreads across the surface instead of beading, and a saturated face fabric blocks vapour from escaping no matter how good the membrane underneath is. You feel clammy, you assume the jacket has failed, and you start looking at new jackets.

It has not failed. It is dirty. Wash it with a technical wash, tumble dry it low for twenty minutes to reactivate the DWR, and reproof it if that is not enough. This is the single most useful thing you can know about a shell, and it is why our care instructions tell you to wash it more, not less.

The short version

• 2L makes room for insulation. Best for constant-output days. MURMUR™.
• 3L is one bonded fabric: tougher, more breathable, no insulation. Best when your output swings. TALON™.
• First number is waterproofing under pressure. Second number is breathability.
• 20K/20K means the shell is not the weak link.
• A shell that has stopped breathing is usually just dirty.