There is little more miserable than a long walk in the British hills with a jacket that turns into a boil-in-the-bag. You stay dry from the rain, but you end up soaked from your own sweat. That is where breathability comes in. A good waterproof jacket is not just about keeping the rain out; it is about letting your body's moisture escape. Get this balance right, and you can enjoy the fells in comfort, whatever the weather throws at you.

Why Breathability Matters on the Hill

When you climb a steep fellside, your body generates a lot of heat and moisture. Even on a cold day, you will sweat. If your jacket cannot let that vapour out, it condenses inside, leaving you clammy and cold when you stop. Breathable fabrics allow water vapour to pass through while blocking liquid water. It is not magic – you will still get damp if you are working hard – but it makes a huge difference. The key is to match your jacket to your level of exertion and the conditions.

Fabric and Membrane Basics

Most waterproof breathable jackets use a laminate: an outer face fabric, a membrane, and often a lining. The membrane is the clever bit. It can be microporous, with holes too small for raindrops but big enough for vapour, or hydrophilic, which moves moisture through a chemical process. For British hills, a hydrostatic head of 10,000mm to 20,000mm is plenty. Breathability is often given as RET (lower is better) or MVTR (higher is better). Look for RET under 6 or MVTR above 20,000g/m²/24h for active use. A durable water repellent (DWR) finish on the outer fabric stops it from wetting out, which helps breathability.

Pit Zips and Ventilation – Your Secret Weapon

Even the best membrane can struggle when you are pushing uphill with a heavy pack. That is why pit zips – long zips under the arms – are so valuable. They let you dump heat and moisture quickly without taking your jacket off. Look for two-way zips that you can open from the top or bottom. Some jackets have mesh backing behind the zip, which stops the flap from gaping but still allows airflow. Other ventilation options include chest pockets with mesh lining, which double as vents when open, and adjustable cuffs that you can loosen to let air flow up your sleeves. In practice, mechanical ventilation often beats breathability alone. Do not underestimate it.

Hoods, Cuffs and Hem – Keeping the Elements Out

A jacket is only as good as its fit and adjustment. A hood that flaps in the wind or drips water down your neck is useless. Look for a hood with multiple adjustment points:

• A rear volume adjuster
• Side drawcords
• A wired peak that you can shape

It should fit over a hat but not restrict your vision. Cuffs need to seal around your wrists, ideally with hook-and-loop tabs that you can tighten or loosen. The hem should have drawcords so you can cinch it down to stop drafts and rain blowing up. When trying a jacket, wear your usual hill layers and put your rucksack on. Check that you can move your arms freely and that the hem does not ride up. A good fit is worth more than any technical rating.

Packability and Weight – Space in Your Rucksack

If you are a fair-weather walker, you might carry your jacket more than you wear it. In that case, packability matters. A lightweight jacket that stuffs into its own pocket is a joy to carry. But beware of sacrificing too much durability. Ultralight fabrics can be delicate and may not survive a scrape against rock or a barbed wire fence. For most British hillwalking, a jacket weighing between 300g and 500g is a good compromise. Look for a stuff sack or a pocket that turns inside out. Also consider how small it packs – a bulky jacket takes up precious room in your rucksack. If you are heading out in winter, you might accept a heavier, more robust jacket for the extra protection.

Caring for Your Jacket – Keep It Breathing

A breathable jacket will not stay breathable if you neglect it. Dirt and body oils clog the membrane and the DWR finish. Wash your jacket regularly with a technical cleaner – never use fabric softener or biological detergent. Follow the manufacturer's instructions, but generally a warm machine wash and a low tumble dry can reactivate the DWR. If water stops beading on the surface, reproof it with a spray-on or wash-in product. Store your jacket clean and dry, and avoid cramming it into a tight space for long periods. With a bit of care, a good jacket will last for many seasons of fell walking.