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There are few subjects more divisive and hotly debated among climbers and hillwalkers than waterproofs.

This article was inspired by the no-nonsense frankness of Andy Kirkpatrick and offers a general view of the choices available to the consumer and how some of the proprietary technologies on offer work.

https://www.andy-kirkpatrick.com/articles/view/the_truth_about_breathable_waterproofs

https://www.andy-kirkpatrick.com/blog/view/staying-dry-when-wet

A waterproof jacket is often the biggest single purchase a mountain sports enthusiast will make. That insidious, cold breaching of your shell layer is so disheartening on a day in the hills, so people aren’t averse to spending hundreds of pounds on them. But how do waterproofs work? Why do they sometimes not work? Is there, as manufacturers might have us believe, such a thing as a magic bullet garment, that will keep you completely dry whilst allowing your perspiration to escape?



First let’s consider the options available:


1. Non-permeable garments. Garments that do not allow any liquid or vapour to pass through them in any direction. Examples include fisherman’s Oil Skins, dry suits and waxed jackets. Completely waterproof. Sweat condensing on the inside of the garment cannot escape, wetting the wearer. Water transmits heat 20 times more efficiently than air, opening the door to hypothermia. These have been superseded by Membranes and Analogy Fabrics for active mountain wear.

2. Membranes. Materials such as Gore-Tex, eVent and Pertex Shield allow water in vapour form to pass through tiny pores, but do not allow liquid water through. The Polytetrafluoroethylene (mercifully abbreviated to ePTFE) membrane is laminated to 1 or 2 additional fabrics to add comfort and abrasion resistance.




Typical construction of a membrane fabric. The membrane layer allows water (e.g. perspiration) in vapour form to pass from the inner to the outer surface, while preventing ingress of liquid water. Additional layers of varying thicknesses are laminated to the membrane for next-to-skin comfort and abrasion-resistance.

3. Analogy Fabrics. 'Directional' fabrics, constructed of threads of varying diameters, utilise capillary action to move liquid water away from the wearer. Developed by Nikwax Analogy and their sister company Paramo. As with membranes these are multi-layered: the next-to-skin layer acts as a ‘pump’ while outer layers provide wind- and abrasion-resistance.




Capillary Action: Directional fabrics use the physical properties of water to move it from the inner to the outer surface of the fabric.

Do waterproofs conform to any standard?


Within the EU there is a standard for waterproof garments. If you're wearing Personal Protective Equipment (PPE) that's also waterproof you're in luck (which may help you overcome the embarrassment of looking like a deckhand on the hill). Look for the CE (Conformité Européene) mark or EN (European Norm) number on the conspicuous garment's label.

EN343 covers clothing providing Foul Weather Protection. Resistance to water penetration and water vapour resistance (waterproofing and breathability in hill parlance) are the properties tested under EN 343. Compliant garments are categorised from 1 to 3, where class 1 offers little protection and no breathability, while 3 “provides the highest level of foul weather protection (and) the highest level of breathability”, more on how these conclusions are reached later.

A garment rated as CLASS 3 under EN343 carries the following label:


But before you rush to inspect your jackets know this: attaining EN standard is not required. And judging by the jackets out on the hill, is not demanded by consumers. We're happy to take the manufacturers' word on the effectiveness of waterproof garments, and we're not as bothered about getting wet as we are about falling: I would not buy a rope or rock anchor that did not conform to the appropriate EN standard.

I bought my waterproofs (Paramo Velez Smock, Rab Latok Jacket, Rohan Deluge Jacket; Patagonia H2NO Trousers) from high street outdoor retailers, and not one of them boasts the above labelling. So how do the manufacturers test their garments and what assurances do they offer consumers?

How are Membrane Fabrics tested?


Water resistance is typically measured using a hydrostatic pressure test in a lab. On one of the tags affixed to that tempting jacket you may find mention of its 'Hydrostatic Head'.

A Hydrostatic Head of 5000mm means that a piece of the fabric should hold a column of water that is 4999mm tall before ingress occurs. The higher the number the greater the water resistance. Patagonia (https://eu.patagonia.com/gb/en/h2no.html) confess that "the tests we create in the fabric lab can’t simulate Mother Nature perfectly". They aim for 20,000mm minimum for their new waterproofs nevertheless.

Breathability is the promise of membrane garments. Not only will they prevent water ingress from outside, they'll allow your vaporous perspiration to pass through the fabric leaving you nice and dry. In the lab, breathability (also known as Moisture Vapour Transfer Rate, MVTR) is expressed in g/m²/24hrs (whatever that is; is that how you measure it on the hill?). Manufacturers use one of 3 tests: the ‘Upright Cup’ test, the ‘Inverted Cup’ test, and the ‘Sweating Hot Plate’ test. The cup tests are similar, each measures the volume of moisture vapour passing through the fabric into a cup in 'optimal conditions' (see below).

The more commonly used Sweating Hot Plate test replicates both the heat loss and moisture evaporation processes from an active body and measures the rate at which both pass through the membrane.

In the real world, effective breathability relies on three assumptions:

1. That there's an optimum temperature/pressure gradient between the inner and outer surfaces of the garment to encourage MVTR. Ideally, it'll be warm and moist on the inside and cool and rainy on the outside (so much for when it rains on a hot, humid day...)

2. That the wearer becomes neither so hot and sweaty as to overwhelm the membrane's capacity to transfer vapour to the outer surface or so cold that the vapour transfer process chills the body through convection.

3. That the garment is neither so soiled with dirt nor so wet on the surface that the membrane is prevented from working, trapping your sweat inside.

As Rab say: "Even the most breathable systems will be less efficient when the outside atmosphere is full of water, so aside from lab-based measurements, thorough field testing plays a central role in the design and development of our breathable garments." The aforementioned tests are therefore used concurrently with field testing and simulated conditions in ‘Rain Rooms’.

How are Analogy Fabrics tested?


Since the construction of the fabric redirects water rather than blocking it, the hydrostatic head test is a misleading gauge of performance. Paramo conduct extensive field testing and Rain Room tests simulating rain “5 times the intensity of normal heavy rain in the UK”. Paramo promise water resistance for 4hrs in rain drops from 0.5mm to 3.5mm falling at 15mm per hour.

What measures can you take to maintain water resistance?


The hydrostatic head test is a measure of the fabric’s water resistance, not the overall performance of the garment. So as well as the materials used, we must also consider the design and construction of the garment. The weakest parts of your jacket are the seams and those pesky holes necessitated by the sub-optimal anatomy of the human body. So, look for taped seams on a membrane, or even laser welded seams if you've money to burn. Is the hood large enough for your needs? Can the sleeves and waist be tightened? Construction, rather than materials, is where your money usually goes.

Help the fabric do its job most effectively: batten down the hatches, and don't look up or reach up if you want to stay dry. The presence of pit zips on so many jackets is the manufacturer's way of telling you to ventilate if you want to optimise functionality and stay dry. Paramo boast of the myriad ventilation options available to the wearer, essential since the multi-layer construction increases the risk of overheating.

Your membrane garment might also boast something called a DWR (Durable Water-repellent Finish), a hydrophobic chemical coating applied to the exterior of the fabric that causes rain to 'bead' on the surface and run off easily. The less water is on the surface, and the less time that water stays in contact with the surface, the more effectively the membrane can work. Some manufacturers use perfluorochemicals (PFCs) in these treatments, now slowly being superseded by more environmentally friendly compounds. Increasingly, garments and treatments declare themselves ‘PFC-Free’ but be sure to check before purchase. This coating works, but not for long (did we say durable?), and the burden of maintaining it is on you. Manufacturers recommend you apply a spray-on or wash-in reproofing agent when you notice a drop in beading.

Paramo garments require regular wash-in treatment to maintain function; expect to treat them 3 times a year. Soiling of the fabric affects function of all waterproofs, so be sure to clean your garment regularly anyway, especially if you notice any reduction in performance.

To wash, use pure soap flakes or a proprietary product such as Nikwax Tec Wash for all waterproofs, never use biological agents and always put the garment through a rinse cycle to remove detergents after washing.

Choose the appropriate garment for your activity: don’t wear a lightweight jacket for a Winter traverse of the Cairngorms or a 3-layer jacket for a Summer mountain marathon.

Accept that accidents happen: Investing in a tube of SeamSeal and some adhesive patches for repairs in the field could save you an uncomfortable time and make you a hero to others.

It may seem counter-intuitive that a garment often marketed as a magic bullet needs so much maintenance and active management. Rare manufacturing faults aside, the technology works, and the key word is system: you are part of it, actively managing to get the best from yourself and your garments.

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