Why British hills ask more of a jacket than you might think

A jacket that keeps you dry on the walk to the shops is not necessarily the jacket you want on a Cairngorm plateau in February. British hill weather is rarely just rain. It arrives sideways, driven by wind, and often just as you have warmed up on a steep pull. The temperature sits around the point where you sweat on the ascent and chill on the summit, and the rain can start and stop three times in an afternoon. That combination — persistent wet, swinging temperatures, and your own body heat — is what makes choosing a waterproof jacket more interesting than it first appears.

The goal is not simply a jacket that resists water. It is one that keeps rain out while letting your own moisture escape, so you stay dry from both directions. Those are competing demands, and every feature below is really a way of negotiating between them.

Breathability, not just waterproofing, should drive your choice

Manufacturers quote two headline numbers. The first is the hydrostatic head, in millimetres: how tall a column of water the fabric holds before it leaks. For hillwalking, 10,000mm upwards is genuinely adequate, and 20,000mm is comfortable for all-day Scottish or Lakeland rain. Past a certain point, breathability matters far more than an extra 10,000mm you will never test.

The second number is breathability, expressed in grams of water vapour per square metre over 24 hours. Look for 10,000g or more for active hillwalking, ideally 15,000g to 20,000g if you walk hard or run hot. A 20,000mm jacket that cannot breathe leaves you soaked from the inside on a long climb — colder and more miserable than being rained on.

Construction matters too. A two-layer jacket uses a separate loose lining: heavier and bulkier. A two-and-a-half-layer jacket has a printed or sprayed lining protecting the membrane — light and packable, but clammy against the skin. A three-layer jacket bonds the membrane to both a face fabric and an inner liner: the most durable, the most comfortable, and the best all-round choice. If you walk regularly in the hills, three-layer is usually worth the extra cost.

Pit zips: the simplest fix for overheating

No membrane can keep pace with a steep ascent under a heavy rucksack. That is why pit zips — long vents under the arms — punch well above their weight. They let you dump heat without unzipping the front and letting rain in, so you can regulate temperature on the move rather than stopping to strip layers.

Look for zips of at least 25cm, ideally longer, with a flap or storm guard over them. Two-way zips are a small luxury, letting you open a vent from either end. If you run hot or climb a lot, this one feature will do more for your comfort than any upgrade in fabric technology.

The hood is where cheap jackets give themselves away

You will wear the hood more than almost any other part of the jacket, and a bad one is genuinely miserable. Three things to check:

• Volume adjustment at the back of the head, so the hood moves with you rather than pivoting over your eyes when you turn.
• A wired or stiffened peak that holds its shape in wind and keeps rain off your face — floppy peaks collapse and funnel water down your neck.
• Face and neck cinches that close snugly without strangling you, and a cut that fits under a helmet if you climb or bike as well as walk.

Try it on over the layers you actually wear, with the hood up, and turn your head side to side. If it blinds you or the peak folds, it will annoy you for years.

Fit, pockets and the details that add up

A hillwalking jacket should fit over a base layer and a midlayer without billowing, and it must let you raise your arms overhead without the hem riding up to your ribs. Check the length: you want the hem to sit below the hip bone, and ideally below a rucksack belt or harness.

• Pockets: two hand pockets placed above a rucksack hip belt, plus one internal pocket for a map or phone.
• Cuffs: adjustable, and wide enough to go over gloves without a fight.
• Main zip: a storm flap, and ideally a two-way zip for venting.
• Weight and packability: a jacket left at home is useless — be honest about whether you want 300g or 600g.
• Durable water repellent (DWR): the finish that makes rain bead and roll off. It wears out long before the membrane does.

Look after it and it will look after you

Most "leaking" jackets are not leaking at all; their DWR has given up, so the outer fabric wets out and feels cold and heavy even though no water is getting through. Wash the jacket with a technical cleaner, never fabric softener, then reproof the DWR with a wash-in or spray-on treatment, and tumble dry on low if the label allows — gentle heat reactivates many finishes.

Rinse off mud and salt, store it loosely on a hanger, and avoid cramming it damp into a stuff sack for weeks. Do that and a good three-layer shell will give you a decade of British hill days — sideways rain, sudden sun and all.