Gear Waterproofs? Don’t Sweat It….. Staying dry is the easy part, says Andy Callan
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nce upon a time, before things got complicated, waterproofs were only that – waterproof and nothing else. You avoided putting them on for as long as possible, because as you flogged your way uphill the condensation inevitably built up inside and you began to overheat. Neither had anywhere to escape to, so you began to stew in your own juice like a boil-in-the-bag meal. Then along came W.L. Gore with his fabric developed for astronauts and things started to change. Yes, these first-generation breathables were bug-ridden – an inability to handle our dirty, sweaty, whiney, money-back bodies was an obvious flaw, but things have moved on to the point where even first-time novices now begin hillwalking with some form of breathable rainwear. Firstly let’s debunk the biggest breathable myth; these fabrics can’t stop you from sweating, which is the body’s natural reaction to exertion, intended to cool the body. The layering system that we talk about is meant to progressively move the sweat (moisture) away from the skin, keeping you dry(ish!) and comfortable. This can only happen if you use wicking fabrics; any cotton-based garment will simply hold the sweat and render all your high-tech clothing useless. Obviously this process is impeded by things like rucksacks which will cause large damp patches – not the fabric’s fault at all. Next up – these fabrics don’t ‘breathe’. They transfer body moisture between their surfaces by means of pressure gradient. As you exercise, temperature and humidity build inside the jacket, driving the moisture through the fabric’s pores to the cooler outside surface where it evaporates. This evaporation is affected by various things, such as how clean the garment is, (always follow the care label), or if the outer face is soaking wet. The major factor which affects moisture transmission is HUMIDITY. If it’s warm and humid outside the jacket, this reduces the pressure gradient and the force which drives vapour to the outside. Moisture then starts to gather in the wicking layers and you feel damp or wet if the sweat can’t be moved fast enough. When this happens you need to stop, ventilate and drop
a layer. So what makes a breathable fabric waterproof? Well, that depends on what you actually consider waterproof. It’s possible to make a fabric with a weave tight enough to keep water out in all but the worst conditions; this can be improved by using chemical water repellents, so you can also reproof it when required. This is how garments such as Paramo, Furtech and Buffalo work, and because they’re simple and easy to care for, they can be recommended, their only drawback being they’re warmer and heavier than equivalent garments from other manufacturers. Truly breathable fabrics use either hydrophilic (water-loving) or microporous materials, either as a coating (i.e. Triplepoint) or a laminated film (i.e. Scantex). Bi-component materials are a combination of both (i.e. Gore-Tex). An explanation of how these fabrics work would fill the magazine, bore you to tears and leave you none the wiser. And where manufacturer’s performance claims are concerned, Disraeli’s dismissive ”Lies, damn lies and statistics” comes to mind. What do they all mean? Not much, since most figures quoted by manufacturers are the results of different tests and obviously enough each will quote the figures that show their fabric in the best possible light. But here’s my ‘Noddy’s Guide’ to the most common tests used.
MVTR
Moisture Vapour Transformation Rate measures how quickly the fabric moves moisture from the inner to outer surface – can be tested by different methods which obviously gives different results.
Hydrostatic Head
Imagine a column of water measured in millimetres sitting on top of a swatch of fabric. The figure given is the largest amount of water the fabric will withstand. This gives a good measurement of waterproofing in a static situation such as sitting on a wet surface.