You’re in Cotswold Outdoor, holding two waterproof jackets. One says “10,000mm hydrostatic head.” The other says “20,000mm.” The second one costs £150 more. The sales assistant mentions something about breathability ratings and taped seams, and now you’re wondering if you actually need a degree in textile science to buy a coat for walking the dog in the rain.
In This Article
- What Is a Hydrostatic Head?
- Waterproof Ratings Breakdown
- Breathability Ratings Explained
- The Relationship Between Waterproofing and Breathability
- Membrane Technologies: Gore-Tex and Alternatives
- Seam Sealing: The Detail That Matters
- DWR Coatings: Your First Line of Defence
- What Rating Do You Actually Need?
- How Ratings Change Over Time
- UK Brands and Their Typical Ratings
- Frequently Asked Questions
What Is a Hydrostatic Head?
The hydrostatic head (HH) is the standard measurement for how waterproof a fabric is. The test is beautifully simple: a column of water is placed on top of the fabric, and the height (in millimetres) at which water starts pushing through tells you the rating.
How the Test Works
A piece of fabric is clamped under a tube. Water fills the tube from the top, gradually increasing pressure on the fabric. When three droplets penetrate through, the height of the water column becomes the HH rating. A 10,000mm rating means the fabric resisted water pressure equivalent to a 10-metre column of water before leaking. That’s a lot of pressure — far more than rain alone generates.
What Counts as “Waterproof” in the UK
Under UK and EU regulations, a fabric needs an HH of at least 1,500mm to be legally called “waterproof.” Most decent outdoor jackets start at 5,000mm and go up to 28,000mm or higher. For comparison, sitting on wet grass generates about 2,000mm of pressure, and kneeling on wet ground pushes around 5,000mm. The pressure from rain falling on your shoulders? About 1,000mm. I learned this the hard way on a wet weekend in Snowdonia — my 5,000mm jacket held up in the rain but soaked through at the elbows where my pack straps pressed the fabric against my arms. The numbers make more sense when you understand that body pressure — not rain — is what usually defeats a jacket.
Waterproof Ratings Breakdown
5,000mm — Light Use
Fine for short walks in light rain. Budget jackets at £30-60 from Decathlon or Mountain Warehouse typically sit here. They’ll keep you dry for an hour or so in moderate rain, but sustained downpour or heavy wind-driven rain will eventually soak through. For school runs, dog walks, and festival standby duty, 5,000mm is adequate.
10,000mm — General Hiking
The sweet spot for most UK hikers. A 10,000mm jacket handles several hours of steady rain comfortably. This is where you’ll find the mid-range hiking jackets from Berghaus, The North Face, and Craghoppers. Expect to pay £80-150. Sufficient for day walks in all but the most brutal conditions.
15,000-20,000mm — Serious Outdoor Use
Mountain walking, multi-day hikes, and Scottish winter conditions. These jackets use more sophisticated membranes and construction. Rab, Arc’teryx, and Montane operate in this space at £150-300. If you’re regularly out in the Lake District, Snowdonia, or the Scottish Highlands, this is the range that won’t let you down.
20,000mm+ — Expedition and Alpine
Designed for sustained heavy rain, snow, and extreme conditions. The extra waterproofing comes with better breathability too — these membranes are the most technologically advanced. Arc’teryx Alpha and Rab Latok jackets at £300-500 sit here. Unless you’re mountaineering or doing multi-day expeditions in winter, you won’t need this level.
Breathability Ratings Explained
Breathability measures how well a fabric lets moisture vapour (your sweat) escape from inside to outside. This matters as much as waterproofing — possibly more for active use.
MVTR: Moisture Vapour Transmission Rate
Measured in grams per square metre per 24 hours (g/m²/24h). A rating of 10,000 means the fabric can pass 10,000 grams of moisture vapour per square metre in a day. Higher numbers mean more breathability. Below 5,000 and you’ll feel clammy during any exercise. Above 15,000 and most people stay comfortable even during hard hikes.
RET: Resistance to Evaporative Transfer
An alternative scale where lower is better. A RET below 6 is excellent breathability, 6-13 is good, and above 20 is poor. Some European brands use RET instead of MVTR, which makes comparison confusing. The key thing: low RET = high breathability.
Why Breathability Numbers Lie
Lab tests measure breathability in controlled conditions — fixed temperature, fixed humidity, no wind. Real-world breathability depends on the temperature difference between inside and outside the jacket, how much humidity is already in the air, and how much wind is pushing moisture away from the outer face. A jacket rated at 20,000 g/m²/24h might feel no more breathable than a 10,000-rated one in humid summer conditions. Take the numbers as relative indicators, not absolutes.
The Relationship Between Waterproofing and Breathability
The Engineering Trade-Off
Making a fabric more waterproof typically makes it less breathable, and vice versa. The holes in a membrane that let moisture vapour out also let water in if they’re too large. Premium membranes manage this balance better, which is largely what you’re paying for when you spend more.
Budget Jackets: Good at One, Bad at the Other
A £40 jacket with 5,000mm waterproofing and 3,000 breathability will keep rain out for a while but feel like wearing a bin bag during any exertion. You’ll get wet from sweat instead of rain — which defeats the purpose. This is the most common complaint about budget waterproofs and it’s entirely predictable from the specs.
What “Good Balance” Looks Like
For UK hiking, aim for at least 10,000mm waterproofing paired with 10,000+ breathability. This combination costs roughly £80-150 but delivers genuine all-day comfort in British conditions. After testing jackets across several brands over multiple seasons, the 10K/10K minimum is where I’d draw the line for anyone doing more than casual walks.
Membrane Technologies: Gore-Tex and Alternatives
Gore-Tex
I’ve owned Gore-Tex jackets from three different brands over the years, and the consistency is what stands out — they just work. The most recognised name in waterproof fabrics. Gore-Tex membranes use expanded polytetrafluoroethylene (ePTFE) with microscopic pores too small for water droplets but large enough for vapour. Their standard “Gore-Tex” membrane is rated around 28,000mm HH. The premium options — Gore-Tex Pro and Gore-Tex Active — add durability or breathability depending on the intended use.
- Gore-Tex (standard) — 28,000mm HH, good breathability. Found in jackets £150-250.
- Gore-Tex Active — lighter, more breathable, slightly less durable. Designed for high-output activities like trail running.
- Gore-Tex Pro — most durable, most waterproof, but heavier. For mountaineering and sustained exposure.
Nikwax Analogy: What About PFC-Free Options?
Environmental concerns about the fluorocarbons in traditional membranes have pushed the industry toward PFC-free alternatives. These perform well but currently don’t match the longevity of traditional membranes. If environmental impact matters to you — and it should — look for brands explicitly marketing PFC-free DWR treatments and membrane technologies.
Brand-Specific Membranes
- Berghaus Hydroshell — 20,000mm HH, strong breathability. Berghaus’s proprietary alternative to Gore-Tex, often cheaper for equivalent performance.
- Rab Proflex/Pertex Shield — excellent breathability, lightweight. Popular for fast-and-light hiking.
- The North Face Futurelight — nanospun membrane claiming exceptional breathability. Real-world reviews are mixed but improving.
- Patagonia H2No — solid 20,000mm performer with good environmental credentials.
- Columbia OutDry Extreme — puts the membrane on the outside, eliminating the need for DWR coating entirely. Interesting approach that works but feels different.
Seam Sealing: The Detail That Matters
Fully Taped Seams
Every stitch hole in a waterproof jacket is a potential leak point. Fully taped seams have waterproof tape bonded over every seam on the inside. This is non-negotiable for any jacket you plan to wear in sustained rain. Every jacket above £80 should have fully taped seams — if it doesn’t, put it back.
Critically Taped Seams
Budget jackets sometimes tape only the most exposed seams (shoulders, hood, upper back) and leave less critical areas untaped. This saves manufacturing cost and is adequate for light rain, but water will find those untaped seams during heavy or wind-driven rain. Check the label — “critically taped” means “not fully taped.”
Welded Seams
Premium jackets increasingly use ultrasonic welding instead of stitching. No needle holes means no tape needed and a cleaner, lighter construction. You’ll find this on high-end Arc’teryx and Rab models. It’s the best option but commands a premium.
DWR Coatings: Your First Line of Defence
What DWR Does
Durable Water Repellent is a chemical coating applied to the outer fabric that makes water bead up and roll off rather than soaking into the face fabric. Without DWR, the outer fabric absorbs water (called “wetting out”), which blocks the membrane’s breathability even though it doesn’t leak through. A jacket with worn-out DWR feels clammy and heavy despite being technically waterproof.
When DWR Fails
DWR degrades through washing, abrasion, dirt, and UV exposure. After 20-30 washes or a season of regular use, you’ll notice water no longer beading cleanly. The jacket starts looking dark and saturated on the shoulders. This doesn’t mean it’s leaking — the membrane still works — but breathability drops noticeably and the jacket feels heavier.
Reproofing Your DWR
Wash with a tech wash (Nikwax Tech Wash or Grangers Performance Wash) to remove dirt that blocks the DWR. Then reproof with a spray-on or wash-in treatment. Nikwax TX.Direct is the most popular in the UK — about £8 from Go Outdoors or Amazon. Reproof every 3-6 months of regular use. It takes 20 minutes and makes a worn jacket perform like new. I reproof my Berghaus Deluge Pro twice a year and it’s still going strong after three seasons — proof that maintenance matters more than buying expensive.
What Rating Do You Actually Need?
Casual Use and Dog Walking
5,000-10,000mm waterproofing, 5,000+ breathability. A £40-80 jacket from Decathlon, Mountain Warehouse, or Regatta handles everyday UK rain. Don’t overthink it for nipping to the shops or 30-minute walks.
Day Hiking in the UK
10,000-15,000mm waterproofing, 10,000+ breathability. This is where you want to invest. A Berghaus Hillwalker or Craghoppers Kiwi at £100-150 will handle 90% of UK hiking conditions. Pair with proper layering and you’re covered for everything short of mountain winter walking.
Mountain Walking and Multi-Day Treks
15,000-20,000mm waterproofing, 15,000+ breathability. Rab Downpour, Montane Ajax, or a Gore-Tex jacket from Berghaus at £150-250. When you’re 6 hours into a Snowdon horseshoe and the weather turns, this is the range that keeps you safe and comfortable.
Winter Mountaineering and Expeditions
20,000mm+ waterproofing, maximum breathability. Gore-Tex Pro or equivalent. Rab Latok, Arc’teryx Alpha, or Mountain Equipment Makalu at £300-500. Overkill for summer hiking but essential when conditions are genuinely dangerous.
How Ratings Change Over Time
New Jacket Performance
Your jacket’s ratings are measured when the fabric is new and the DWR is fresh. Real-world performance starts declining from the first wear. This isn’t a defect — all waterproof fabrics degrade with use, washing, and UV exposure.
The First Year
DWR effectiveness drops noticeably after 10-15 washes. Breathability may reduce by 20-30% as the membrane accumulates body oils and detergent residue. Regular tech washing (every 5-6 wears) and reproofing maintains performance. Most people skip this maintenance and then blame the jacket for “leaking” when it’s actually wetting out.
Long-Term Durability
A quality Gore-Tex jacket maintained properly lasts 5-10 years of regular use. Budget membranes may degrade in 2-3 years. The membrane itself rarely fails — it’s the DWR coating and seam tape that give up first. Seam tape can be repaired at specialist services like Nikwax or directly through some brands.
UK Brands and Their Typical Ratings
Here’s where the major UK-available brands typically fall:
- Mountain Warehouse — 5,000-10,000mm HH. Budget-friendly at £30-70. Adequate for casual use.
- Regatta — 5,000-15,000mm HH. Good value mid-range at £40-100. The Birchdale is a solid budget hiker.
- Craghoppers — 10,000-20,000mm HH. British brand, excellent fit for UK conditions. £60-150.
- Berghaus — 10,000-28,000mm HH. The Hillwalker range is a UK hiking institution. £100-300.
- Rab — 15,000-20,000mm HH. Sheffield-based, premium quality. £150-350.
- The North Face — 10,000-28,000mm HH. Wide range from casual to technical. £80-350.
- Arc’teryx — 20,000-28,000mm+ HH. Premium Canadian brand, exceptional quality. £250-600.
- Montane — 15,000-20,000mm HH. Great lightweight options. £120-300.
Frequently Asked Questions
Is 10,000mm waterproof enough for UK hiking? For most day hikes in lowland and hill country, yes. A 10,000mm jacket handles steady rain for several hours. If you’re heading into mountain environments or doing multi-day treks in exposed areas, step up to 15,000-20,000mm for extra security.
What’s more important — waterproofing or breathability? For active use like hiking, breathability matters more than extreme waterproofing. A 10,000/15,000 (waterproof/breathable) jacket is more comfortable than a 20,000/5,000 one. Getting wet from sweat is just as miserable as getting wet from rain, and a breathable jacket prevents that.
Why does my waterproof jacket feel wet inside? Most likely the DWR coating has worn off, causing the outer fabric to wet out. This blocks the membrane’s breathability, trapping your body moisture inside. Wash with tech wash and reproof with Nikwax TX.Direct or similar — it usually solves the problem completely.
Do I need Gore-Tex specifically? No. Gore-Tex is excellent but brand-specific alternatives like Berghaus Hydroshell and Rab’s Pertex Shield perform comparably at lower prices. The membrane brand matters less than the overall waterproof and breathability ratings. Check the numbers rather than fixating on the label.
How often should I reproof my jacket? Every 3-6 months of regular use, or whenever water stops beading on the outer fabric. A quick test: hold the jacket under a tap. If water soaks into the face fabric instead of beading and rolling off, it’s time to reproof. The process takes 20 minutes and costs about £8 for a bottle of Nikwax TX.Direct.