How to choose a waterproof jacket: ratings, breathability and fit

By Kenny Stocker 08 Jan 2026 13 min read

What 10K, 20K and 30K waterproof ratings mean, why breathability matters as much, and which of our waterproof jackets suits walking, running or the mountains.

A waterproof jacket keeps rain out with a waterproof layer in the fabric and taped seams, and lets the water vapour from your sweat escape so you don't get wet from the inside. How well it does the second part matters as much as the first.

The short answer: for walking in the UK, a 3-layer jacket rated around 20,000mm waterproof with good breathability covers most days. Go lighter if you're running or only carrying it for showers. Go tougher if you're heading into the mountains in winter.

Testing jacket waterproofing in the Peak District — Testing waterproofs in the Peak District rain

In this guide

What makes a jacket waterproof
Waterproof ratings: what 10K, 20K and 30K mean
Breathability and why you can get wet inside
2.5-layer and 3-layer jackets
Choosing a waterproof for your activity
Hood, pockets, vents and fit
When you don't need a full waterproof
Looking after your waterproof
Our waterproof jackets and what each is for

What makes a jacket waterproof

A waterproof jacket has three things working together. A waterproof membrane or coating inside the fabric stops liquid water getting through. Taped seams stop it coming in through the stitching. And a water-repellent finish on the outside, called DWR, makes rain bead up and roll off.

Water-resistant, showerproof and windproof jackets don't have all three. The fabric may shed a shower, but the seams aren't taped and there's often no hood. They're lighter and more breathable, and fine for short showers and fast days.

To tell whether a jacket is waterproof, look for a hydrostatic head rating and taped seams. No jacket keeps you perfectly dry in every situation. Rain finds its way in at the cuffs and the hood if they're not done up, and on a hard climb you'll sweat more than any fabric can let out. A good waterproof keeps those to a minimum.

Waterproof ratings: what 10K, 20K and 30K mean

Hydrostatic head (HH) is a lab test. It measures how tall a column of water, in millimetres, the fabric holds back before water comes through. A 20,000mm (or 20K) fabric holds back a column 20 metres high.

Rain on its own doesn't press hard against a jacket. The higher numbers matter where something pushes water through the fabric: rucksack straps on your shoulders, kneeling or sitting on wet ground, and fabric that's worn after years of use. A higher rating gives you more margin at those points.

Is 10,000mm waterproof good? It's a sensible minimum for a jacket you'll wear in steady rain, and fine for walks where you won't carry a heavy pack for hours.

Is 20,000mm waterproof good? Yes. It gives plenty of margin for long wet days with a rucksack, which is why it suits UK hillwalking.

What about 30,000mm? That's a lot of margin, usually found on tough mountain shells built for harnesses, heavy packs and winter weather. Our Definition is rated 30K.

The rating is for the fabric when new. Seams, zips and how the jacket is put together matter too, which is why taped seams and a good hood are part of the picture.

Breathability and why you can get wet inside

When you work hard, you sweat. A breathable jacket lets the water vapour from that sweat pass out through the fabric. A jacket that doesn't breathe, like a plastic poncho, keeps rain out but leaves you damp from the inside.

Breathability (MVTR) measures how much water vapour, in grams, passes through a square metre of fabric in a day. Higher is better. Brands use different test methods, so compare MVTR figures within one brand rather than across them.

Two things often make a good jacket feel like it's leaking:

Condensation. When it's cold outside, vapour can turn back into water on the inside of the fabric before it gets out. Breathable fabrics reduce this but can't stop it on a hard climb.
A wetted-out face fabric. When the DWR wears off, the outer fabric soaks up rain. The jacket is still waterproof, but a film of water on the outside blocks vapour getting out, so you get damp inside.

Vents help with both: pit zips, a two-way front zip, and mesh-lined pockets you can open. See why a waterproof can feel like it leaks for more.

2.5-layer and 3-layer jackets

The waterproof membrane needs protecting on the inside, and the two main ways of doing that give two kinds of jacket.

2.5-layer: the membrane has a thin printed or sprayed coating on the inside instead of a full lining. It's lighter, packs smaller and costs less. It's less hardwearing and can feel clammier against bare skin. Good for occasional use and for carrying "just in case".

3-layer: a light fabric lining is bonded to the inside of the membrane. It's tougher, more comfortable next to skin and lasts longer, but it's heavier and costs more. Good if you wear your waterproof a lot, or with a heavy pack. See how waterproof jackets work for more on construction.

Choosing a waterproof for your activity

Everyday walking and occasional showers. A light 2.5-layer jacket is enough. Argonaut (men's) and Atalanta (women's) are 10K/10K, with a relaxed fit for layering and mesh-lined pockets that double as vents.

Hillwalking in the UK. Long wet days, a rucksack and wind on the tops. A 3-layer jacket around 20K. Fortitude is built for this, with a longer cut, a wired-peak hood and a map-sized chest pocket. Sigma has a map-sized pocket too, and is made from a single material so it can be recycled at the end of its life.

Walking in the rain on the Isle of Arran in waterproofs — Walking in the rain on the Isle of Arran, where a hood and a map pocket earn their place

Scrambling, climbing and mountain biking. You need to move freely and fit a helmet under the hood. Balance is 3-layer with some stretch, an active cut and a helmet-compatible hood.

Running and fast days. Weight and breathability matter most. Gravitas is a 3-layer jacket at around 200g (size M), rated 20K/20K.

Running in the ultralight Gravitas waterproof in Snowdonia — Running in Gravitas in Snowdonia: light enough to wear all day, breathable enough to run in

Winter mountains and mountaineering. Harsh weather, harnesses and rock. Definition is our toughest shell: 30K waterproof, a hardwearing nylon 6,6 outer, a helmet-compatible hood and vents that still open with a harness or hip belt on.

Hood, pockets, vents and fit

Hood. A good hood cinches around your face, turns with your head and has a stiff or wired peak to keep rain off your face in wind. If you climb or ride, check it fits over a helmet.

Raincoat wired hood — A wired peak keeps the hood's edge off your face in wind and rain

Pockets. Check you can reach them with a rucksack hip belt or harness on, and that a map fits if you carry one.

Vents. Pit zips and a two-way front zip let heat out quickly without taking the jacket off.

Fit. A waterproof should fit over the layers you'll wear under it on a cold day, usually a base layer and a fleece, without being baggy. Raise your arms: the hem shouldn't ride up past your waist and the cuffs should still cover your wrists. A longer back helps on the hill; a trimmer cut suits running and climbing.

When you don't need a full waterproof

A full waterproof isn't always the best outer layer. Some days call for something more breathable, warmer or tougher.

Windproof. For breezy, mostly dry days when a waterproof would be too sweaty. Cirrus (women's) has a waterproof membrane but untaped seams, so it handles a sudden shower and packs into its own pocket.

Softshell. Stretchy, tough and very breathable, with a water-repellent finish for light showers. Resolute (women's) is a double-weave softshell for days that are cold and windy but mostly dry.

Pile-lined smock. Some hillwalkers and climbers would rather stay warm while damp than try to stay dry. Jura (women's) has a windproof outer over thick Sherpa fleece, worn over a base layer or bare skin, with side vents to let heat out.

Ventile. A tightly woven cotton that blocks wind and sheds rain, and lasts for years. Ranger (women's) is our Ventile jacket. See what Ventile is and how it works.

Insulated waterproof. For cold, wet days when you won't be working hard, like winter walks with lots of stops, skiing, or warming up after a winter swim or ride. Solace (women's Solace Parka) has a 10,000mm waterproof shell with synthetic insulation inside. It's warmer and simpler than separate layers, but you can't take the insulation off if you get hot.

Insulated waterproof jacket — Solace: a waterproof shell and synthetic insulation in one jacket, for cold, wet days with lots of stops

Looking after your waterproof

Wash your waterproof when it gets dirty, because dirt and body oils stop the DWR working. When rain stops beading and the fabric starts to darken, it's time to reproof it. See how to reproof waterproof clothing. Each of our stores has a repair station that can patch holes and fix zips, and we offer a wash and reproof service too.

All our waterproofs have a PFAS-free water-repellent finish. When a jacket reaches the end of its life with you, see our Continuum project for ways to give it a new one.

Our waterproof jackets and what each is for

Argonaut and Atalanta: when you want a light waterproof for walks and showers. 2.5-layer and 10K/10K, with a recycled face fabric (Argonaut's is 100% recycled nylon). Argonaut (men's), Atalanta (women's).

Fortitude: when you're hillwalking in the UK. 3-layer, 20K/20K, longer cut, wired-peak hood and map pocket. Men's and women's.

Sigma: when you want a waterproof that can be recycled. 3-layer, 15K HH and 10K MVTR, made from 100% post-consumer recycled polyester. Every part is made from the same material, so it can be recycled in one stream at the end of its life. For hillwalking, scrambling and riding. Men's and women's.

Balance: when you need to move freely. 3-layer, 20K/25K, stretch, active cut and helmet-compatible hood, for scrambling, climbing and riding. Men's and women's.

Gravitas: when every gram counts. 3-layer, 20K/20K, around 200g, for running and fast days. Men's and women's.

Definition: when you're heading into the mountains in winter. 3-layer, 30K HH and 20K MVTR, nylon 6,6 outer, harness-friendly vents. Men's and women's.

See all waterproof jackets, or waterproof trousers.