Secrets of staying dry

A decent hard shell jacket could be your most important and costly investment in mountain attire… so it’s time to delve into the wondrous world of waterproofing.

Secrets of staying dry

by live for the outdoors |

Every year, Snowdonia, the Lake District and the Scottish Highlands get doused with more than 4 metres of rainfall. It’s no coincidence that most of the UK’s soggiest places are also its pointier bits. Which means that for most UK hillwalkers, a waterproof jacket tends to be near the top of their kit list. But the range available today can be bewildering, not helped by a slew of pseudo-science and confusing marketing hype. It’s probably this barrage of jargon that causes waterproofs to be one of the most misunderstood (and therefore most frequently criticised) bits of outdoor kit. So let’s start our guide to staying dry with some simple explanations of the most common (baffling) terms you’ll come across in gear reviews, or on all those product tags in outdoor shops...

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Jargon buster

How waterproof?

Water-resistant, water-repellent, weatherproof and waterproof. They sound like they mean the same thing, but actually they’re all quite different. A water-resistant fabric has tightly woven fibres that naturally resist penetration by moisture. It might stand up to light drizzle but not heavy rain. A water-repellent fabric has a finish to further enhance its ability to shed water. This might be a wax coating or a durable water repellent (DWR) treatment. Then there are weatherproof fabrics, which aren’t strictly waterproof under laboratory conditions, although they provide decent protection out there in the real world. But a waterproof fabric is lab tested as being impervious to water, even under pressure (up to a point, since there are degrees of waterproofness – see hydrostatic head later on in this guide).

Breathability

As well as the level of water-resistance on offer, breathability is the other critical performance element of a waterproof fabric. Put simply, it’s what enables moisture from inside your jacket to escape, stopping you from becoming a stuffy, clammy mess. It’s a misleading term, because it implies that it has something to do with breathing or air, but actually, in garment terms, breathability simply refers to a material’s ability to move moisture. Remember that it’s still about keeping you dry, not about ventilation or keeping you cool. A breathable jacket doesn’t stop you from getting hot and sweaty, but it should gradually move moisture vapour away to keep you more or less dry and comfortable.

Waterproof membrane

The basis of all hard shell jackets, a membrane is a thin layer that is impenetrable to liquid water but allows moisture vapour to move through it (hence waterproof-breathable, or WP/B). Membranes are usually made of ePTFE (expanded polytetrafluoroethylene) or PU (polyurethane). They are generally laminated to the inside of the face fabric of a jacket and are therefore sometimes referred to as ‘laminates’.

Face fabric

This refers to the outer layer of a waterproof jacket, which is usually made from polyester or nylon. The face fabric protects the membrane from abrasion and dirt, and aids water repellency by providing a surface on which to apply a DWR.

Rain beading on a waterproof jacket
A good DWR casues water to bead up and roll of the surface of the fabric

DWR treatment

AKA a Durable Water Repellent treatment, this finish is largely what causes rain to bead up and roll off your jacket. It’s an essential part of modern waterproofs, because if the face fabric becomes saturated (a process called ‘wetting out’) the membrane cannot breathe effectively, leading to moisture build-up inside your jacket. Unfortunately, Durable Water Repellent treatments are not actually very durable – in fact, they can degrade quite quickly. This is why regularly cleaning and reproofing your waterproofs with specialist products is so important.

Backer or liner?

A backer is used on the inner surface of waterproof-breathable fabrics to protect the membrane and provide extra comfort. A 2-layer jacket has no backer, instead employing a separate mesh or taffeta drop liner. A 2.5-layer jacket uses a raised print or pattern (considered a ‘half-layer’, hence 2.5), while a 3-layer jacket uses a full bonded textured or mesh layer that creates a sort of sandwich, with the membrane in the middle and the face fabric on the outside. 3-layer jackets make for the most durable and effective shells but are also the most expensive. 2.5-layer jackets are cheaper, lighter and more packable, but can sometimes feel a little clammy. 2-layer jackets are comfortable to wear, but the need for a separate liner makes them bulkier and heavier.

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Waterproof fabrics

Waterproof shells typically use an ePTFE- or a PU-based membrane. The first such membrane was Gore-Tex – still the biggest and best-known brand. In 1969, Bob Gore discovered that when PTFE is rapidly stretched, it creates a thin and porous web. Due to molecular composition and surface tension, liquid water cannot pass through, but gaseous moisture vapour can.

Gore-Tex

The UK’s first Gore-Tex waterproof jacket was made by Berghaus in 1977. Gore developed the material by adding a microscopically thin PU coating to the inner surface of the ePTFE membrane. Today, in addition to ‘standard’ Gore-Tex, Gore’s fabrics include Gore-Tex Paclite and Paclite Plus, Gore-Tex Active, Gore-Tex Shakedry and Gore-Tex Pro. The range caters to different user needs, but generally Paclite jackets are the cheapest, intended to be waterproof but also lightweight and compressible. Gore-Tex Active and Shakedry are superlight and highly breathable for fast-paced activities. Gore-Tex and Gore-Tex Pro balance performance and durability, making them suitable for more demanding conditions.

eVent

Like Gore-Tex, eVent is made from ePTFE, but instead of a thin PU inner layer it has an oleophobic (oil-hating) coating to protect the membrane. This retains ePTFe’s open structure and was marketed as ‘direct venting’ technology, being highly praised for its breathability. There are currently three different eVent fabrics on the market, again designed for different users: DVstorm, DValpine and DVexpedition.

PU-based membranes

Polyurethane (PU) membranes are also waterproof, but unlike ePTFE they are non-porous. However, if a PU membrane is thin enough moisture vapour can slowly pass through. Since PU is hydrophilic (water-loving), water vapour molecules chemically bond to the surface and pass through the membrane to the opposite side where they then evaporate. PU membranes tend to be thicker and less breathable than ePTFE membranes.

Their breathability is dependent on external air temperature, plus a high concentration gradient (the inside of your jacket needs to be much more humid than the outside). As such PU-based jackets work best when you’re hot and sweaty, but it is cold and dry outside.

PU membranes are durable and easy to manufacture. Popular PU-based fabrics include Pertex Shield, Dermizax and Porelle. In addition, almost every major outdoor brand now has its own PU-based waterproof-breathable technology. Mountain Equipment’s Drilite, Patagonia’s H2No, Berghaus Hydroshell, Jack Wolfskin Texapore and Mammut DRYtech are all examples. In recent years, some brands have adopted different approaches.

The latest industry developments are ‘electrospun’ or ‘nanospun’ PU membranes, like Polartec Neoshell, Outdoor Research’s Ascentshell and The North Face’s Futurelight. A new way of fabricating membranes, this method makes it possible to create an air permeable material, resulting in lighter, stretchier and cooler garments.

Waterproof fabric construction compared

Alternative technologies

Gore-Tex Shakedry and Columbia OutDry Extreme invert the traditional layered approach and place the membrane on the outside of the garment, negating the need for a DWR. Others have developed stretchy and rustle-free membranes like Rab Proflex, designed for greater comfort and enhanced freedom of movement.

Nikwax Analogy

Other approaches do away with a membrane altogether. The best-known example is Nikwax Analogy in Paramo waterproofs. A DWR-treated polyester face fabric is backed with a ‘pump liner’ that moves moisture away from the wearer via capillary action, or wicking. Unlike a membrane, it can move liquid water (sweat) as well as moisture vapour, and many users swear by its effectiveness. The two-layer construction means that Paramo jackets tend to be warmer and heavier than shells though.

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Comparing performance

Out of all these different fabrics, which one is best? It’s hard to say. There are many variables, including climatic conditions, levels of activity and individual physiology, as well as what you’re wearing underneath your jacket. And while all jackets work pretty well when new, you may see a drop-off in performance a few months or a year down the line.

The fabric is also only one element of a waterproof jacket. That’s why taped or bonded seams, stormflaps and water-resistant zippers are important. Similarly, all jackets have a few critical potential failure points, namely four big holes – one at the end of each sleeve, one at the bottom and the one at the top that you stick your head through. Rain can seep through even the tiniest gap, so a hem drawcord, a decent hood and adjustable cuffs are vital, as is a good fit. Most brands do provide a couple of stats that can help compare the performance of different garments.

Hydrostatic head

The industry standard for measuring waterproofing is ‘hydrostatic head’. In a controlled test, a column of water is placed over an area of fabric. The height of the column (and therefore the water pressure) is increased until water seeps through. Results are expressed in millimetres. For outdoor kit, they range from 1500mm to 30,000mm. That’s 30 vertical metres of water bearing down on the fabric. Pack straps and hipbelts or contact with rocks and the ground all increase the external pressure on the fabric. It is often at these points of contact that moisture will seep through.

Hydrostatic head

Typical waterproof jacket Hydrostatic Head ratings

10,000mm Suitable for everyday hiking in light rain showers. A good benchmark for a hillwalking waterproof.

20,000mm Should stand up to heavya and prolonged rain in most conditions.

30,000mm Waterproof in even the most extreme conditions. Unlikely to leak even at pressure points. However, many brands argue that such a high level of waterproofing is essentially overkill.

Moisture Vapour Transmission Rate (MVTR)

MVTR is one way to assess a fabric’s breathability. Again, these tests are done in a lab under controlled conditions. It measures the rate at which moisture permeates through a fabric, measured in grams per square metre per day. For hillwalking waterproofs, MVTR figures typically range between 5000 and 35,000 – though more impressive figures can be achieved by changing the method by which garments are tested. As such, it’s difficult to objectively rely on MVTR figures.

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What makes the ultimate waterproof?

As climber and gear guru Andy Kirkpatrick once pointed out, the ultimate breathable waterproof already exists. It’s called the umbrella. Unfortunately, wandering around with a brolly in your hand isn’t very practical for hillwalking! But when it comes to choosing a waterproof jacket, use hydrostatic head or MVTR as a rough guide only. Choose a jacket that fits well, has the features you want and not those you don’t, and is designed for your needs – whether that’s summer hillwalking, lightweight backpacking or winter mountaineering. Trail gear reviews are also a decent place to start, since nothing beats all this theory like getting into the hills and doing some practical, real-world testing. Lastly, be mindful of your budget and the sustainability of your gear too. In recent years, chemical DWRs and membranes, particularly those that contain or use perfluorinated compounds (PFCs), have been heavily criticised for their negative environmental impact.

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Six waterproofing tips

1. Get your base layer right

The foundation of staying dry and comfortable all day long is a wicking base layer, because what’s next to your skin makes the biggest difference in performance terms. In fact, save £40 on the cost of your shell and instead spend it on a decent base layer.

2. Don’t overdress

If you’re heading out on a big hill day, be bold and start cold: you’ll soon warm up when you get moving. If you start to sweat early on, you’re immediately creating loads of moisture and placing unnecessary demands on your layering system, even before it’s started raining.

3. Don’t wear a waterproof unless it’s raining

Keep it in your pack, and only put it on if needed. Even the most breathable shell won’t keep you as comfortable as a solid base layer and mid-layer combo. And if it’s windy but mostly dry, a windproof or soft shell jacket is a better choice than a waterproof.

It's much more fun if your waterproofs keep you dry!
It's much more fun if your waterproofs keep you dry!

4. Don’t sweat it

Add or remove layers when necessary. This will help you dump heat fast, minimise sweating and stay comfortable. If you are forced to don your shell, vent it by unzipping the neck, pit zips or mesh pockets. Far more moisture vapour can escape this way than through the fabric alone.

5. Drizzle doesn’t count

With good wicking layers, light drizzle doesn’t require a waterproof, and dampness will soon disappear, especially if you keep moving.

6. Look after your gear

Regular TLC will greatly extend the life of any waterproof fabric. Abrasion, grease and grime all stop waterproof-breathable membranes from working efficiently. If your jacket doesn’t seem to be beading as effectively, clean and reproof your gear with specialist products like Nikwax or Grangers. These rely on the original DWR treatment, as this is what they stick to. So, try and do this regularly, because if the DWR is already worn off, it’s unlikely you’ll ever be able to fully restore it.

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