My Waterproof Jacket Leaks!

You'll have seen the discussions of course. Runner A recommends a jacket as the best he's ever used, then five minutes later Runner B says he had one of those but it leaked like a sieve. They can't both be right............can they? And nowadays we get instructions that we must have hoods, taped seams, this, that, whatever; Joe says how can he find the lightest job that will still satisfy the kit inspectors while Bill says take the heaviest you can carry or you'll die. What's it all about?

Well, for what it's worth, here's my take on the subject. The usual health warnings, my views come from a combination of experience in the hills and training as an engineer; I hope they make sense, I'm sure not everyone will agree, but if they prompt a bit of thought that's enough and OK. Also this is an area where it's easy to get bogged down in the science; I'm hoping to get by with only the most  important bits and I might take some shortcuts which will offend the purists, but I'm sure I'm like most runners in just wanting to understand why things that affect us happen and what we can do to try and control them. And if you've read my blog before you'll know that these odysseys of mine can go on for a while, so be prepared if you're going to stay the course.

First the briefest of histories. When I was a lad, if it rained in the hills we donned our "anoraks" (pullover smocks with a hood and regulation front pocket for OS map) made from cotton with some sort of proofing involved. They were OK in showers and a bit of rain but not great when it got heavy. We got wet. Then nylon appeared with Peter Storm, Henri Lloyd and so on, fully waterproof and it kept all the rain out. The problem was that it kept all the sweat in as well so you got pretty much as wet on the inside as it was on the outside. Then Gortex came along with the first "breathable" fabric and solved the problem. Sort of.

At this point we have to be clear about what a few of the key terms mean:-

1. "Sweating". This is your body's way of dumping unwanted internal heat generated by physical exercise. A fluid that is mainly water is pushed out through small holes in your skin (pores), carrying some heat with it. What happens next depends on external conditions.  If you're wearing no clothes and the air humidity is low, the water (sweat) will evaporate, gaining latent heat from your skin as it goes and so cooling you down. That's the way it's designed to work. But when your body gets hot and generates sweat, it can't control what's happening on the outside. If you wear a technical "wicking" shirt, the sweat gets drawn through to evaporate on the outside, almost as well as without a shirt. A cotton shirt will absorb the sweat, but it will eventually start evaporating from the outer surface, although you won't feel so comfortable. A rucksack tight against your back will prevent any evaporation at all in that area. And if the air outside is already saturated  -  ie it has already absorbed all the water vapour it can hold, a condition known as 100% Relative Humidity (RH)  - then sweat won't evaporate whatever you're wearing.  But we should say here that the air won't have reached 100% RH until you see visible signs of it; the water vapour starts to condense in the air, and you're walking in mist, fog, a cloud (or the bathroom). The fact that it's raining alone does not mean that the air is saturated (but for sure if there is rain about the air will be already holding more moisture that it would have under a cloudless blue sky).

2. "Breathable".  This is generally accepted to be a material which has "holes" small enough to prevent water droplets passing through while big enough to allow the passage of water vapour. This isn't the precise truth, but it's good enough for us here. It doesn't matter what the material is, or how the "holes" are created, these details might affect the overall robustness of the material but not the explanation of how it might work. The theory is that you can wear such a material when it's raining; sweat then evaporates on the inside of the jacket and so can pass out through the holes, which at the same time are not letting the rain in.

3. "Waterproof". A string vest is not waterproof. Wear one in the rain and you'll get wet. A plastic material can be made completely waterproof - think of the bladder in a Camelback - and if you make a jacket out of it, it won't let the rain in, but it won't let any vapour out either, under any conditions. What we think of as modern "waterproof-breathable" materials are a compromise between these two. The smaller the "holes" the more they lean towards waterproof, bigger holes mean more breathable. Maybe they should more correctly be referred to as "water resistant".  A material that is resistant to a steady rain may not be so resistant if the pressure of the water goes up  -  a tropical downpour maybe, or if you sit in a puddle. That's why modern jackets have some sort of hydrostatic rating on the label  -  a measure of their actual degree of waterproofing. In a practical garment, the resistance given by its basic degree of waterproofing can be enhanced (for example by putting a shiny coating on the fibres so that they "shed" water droplets better - this is what has worn off when you are told you need to have the garment "re-proofed"), or compromised (for example by making holes in the seams when they are stitched  - which is why manufacturers claim the improvement of "taped seams" when they have covered up the holes with some glued-on tape).

So far, I would assume that anyone more expert than me might tick me off for over-simplifying things, but would hopefully concede that I haven't said anything outrageously wrong. But it seems to me there are some elephants in the room even up to here. You may already have spotted them, but let's move on now to some propositions on what might actually be happening when you wear your jacket for running out in real weather.

Let's say you are out running on a coolish but not cold day, wearing a long-sleeved technical teeshirt, and it feels pretty comfortable, not too hot, not too cold. The heat you're generating is being dissipated by your sweat into the air. Then it starts to rain steadily. It's not unpleasant to start with, but after a while you start to feel cold. What's happening here is that the raindrops hitting you and then eventually dripping away are more efficient at conducting the heat away than the air was  (you put air gaps into things to improve insulation, remember?), so now you are losing more heat than you're producing and you start to cool down.

There are three options from here. (i) You run faster to create more heat to warm up, (ii) you increase the insulation by putting on a thicker layer, say a fleece, or (iii) you pull on a waterproof. Intuitively, the best option is (iii) so on goes your lightweight waterproof but breathable jacket. This sheds the raindrops much more quickly and efficiently than your teeshirt so it cuts down the heat transfer, and this enables you to warm up. But as you warm up, you start to sweat again, and now the sweat has a much harder route to escape and evaporate. First of all, it now has to evaporate not into unrestricted air, but into the small space between your jacket and the layer inside it. And when it reaches the shell it (a) has to find its way through the restricted holes in the surface, and (b) even if it gets out it will be faced with air more humid than before you put your jacket on. Sorry, but a lot of your sweat is either not going to evaporate, or evaporate then re-condense as it hits the inside of the shell. You probably still feel quite comfortable, because the heat being taken away now matches again that which you are producing by the running effort, but inside your jacket you are unlikely to be dry.

Most outings in the rain start and end like this. When you stop running you get into a warmer place, change your clothes, and think nothing of it. Your jacket did a good job. But on a longish run, there may be the opportunity for a few other things to happen to affect the balance again, such as:

- you get tired, so you slow down to a jog or maybe even a walk, so you're putting less energy (and therefore less heat) into the system, but the outside conditions are still taking out what they did before.

- the weather gets significantly worse, heavier rain, lower temperature, higher wind, so that although you're still putting in the same energy (heat), the outside conditions are taking it away faster.

- it's a long time since you last ate anything, so more of the work you're doing gets used internally and less goes to warm the surface.

The first thing you realise in any of these scenarios is that you're getting cold. Then comes the realisation that your clothes are wet, because instead of being warm and wet which was comfortable, they are now cold and wet which isn't  -  "my waterproof jacket leaks!" Yes, I'm prepared to stick my neck out and say that so long as you're wearing a jacket that claims to be waterproof, then 99% of the moisture on the inside will have come from you, not the sky. OK, nice to know, but once you get into the "I'm cold and wet" scenario experience shows that you're on a downward spiral to ending your participation in the race (and in anything else if you're really unlucky), so what can we do about it? Before we go on to that, let's just home in on a couple of points that are key to the situation.

1. Breathable clothing was originally developed for activities less intense than running, such as walking, climbing and the like, and was found to work well. But these pastimes are less energetic than running and less sweat is necessary. Walkers and climbers would also not normally use a waterproof shell unless it was part of a three (at least) layer system - base layer wicking, to keep sweat away from skin, middle layer insulation (fleece, etc), then outer shell to keep rain or wind out. The whole system is under far less stress than in running, and the wicking/insulation layers hide any deficiencies better - they keep you feeling warm. Further, these activities are often intermittent, where bursts of energy are interspersed with easier or inactive periods allowing any accumulated moisture to evaporate while none is being produced. Finally, walkers and climbers (sensible ones at least) layer up and down frequently to keep in balance with changing conditions, whereas a runner will begrudge the time spent in doing this.

2. There is nothing wrong with being wet. Hot showers and warm swimming pools are not unpleasant, and certainly won't do you any harm. It's being COLD that gets you, and the problem with water is that, as we've seen above, it accelerates the heat transfer away from your body in a big way. The challenge is, if you can't avoid getting wet, how do you minimise the heat transfer?

So where has all this got us so far? You know now that I'm sceptical that you'll stay dry inside any waterproof jacket, whatever it claims, when you run in it. You know that being wet isn't in itself bad, but being wet (especially if it's raining) promotes heat loss, and if you can't manage that heat loss you can get into big trouble. So is there a strategy that we can adopt that might keep us out of jail? Well, for what it's worth, here's mine.

1. Choosing and maintaining a waterproof jacket

I personally don't think there's an overall winning brand; after all they're all using the same science and mainly similar materials. I've tried a lot of the reputable guys, North Face, Salomon, Montane, OMM and can't really detect any difference in performance. Better to go with what fits you best I think. I'm not sure that I buy into the taped seams thing but a lot of Race Directors require it and all of the reasonable makers do it anyway. More important for me is the state of the surface. You want it to shed water drops fast. You can't stop it raining but you want the drops that hit you to bounce off as fast as possible before they pick up any heat on the way. Pour water on your jacket and it should form globules and run off. If it doesn't, time for reproofing (or a shinier material).

2. Don't put on a waterproof unless you really need to

It doesn't matter how brilliantly technical your jacket is, it will be nowhere near as breathable as if you don't wear it. The sweat inside starts building from the moment you put it on. I'm quite happy to carry on in a baselayer in gentle rain, or even a light fleece if it's chilly. In the Lakeland 50 one year we had intermittent showers, some of them quite heavy. I passed numerous runners wearing waterproofs. But each time, often just at the point where I would be thinking "this rain has gone on long enough, I need to put a jacket on", the rain stopped. I ran from start to finish in a long-sleeved Helly-Hansen vest and was comfortable throughout and dry at the end. If it's windy I prefer a very light windproof, much more breathable than a waterproof, and I often carry both for this reason. The moment you put your waterproof jacket on is the moment you've decided to transfer from "cool and wet" to "warm and wet".

3. Once you've got a waterproof on, manage the layers

This won't be popular with the faster runners, but less necessary for them either as they continue to generate plenty of heat energy throughout the race. But if your pace drops to a jog/walk or the conditions worsen, be prepared to play with light teeshirt, long-sleeved teeshirt and light fleece under the waterproof to keep you warm enough but not too warm as the race goes on. Once you're really cold you'll probably have to stop somewhere dry to warm up and regroup before you can carry on. In the 2012 West Highland Way Race it rained pretty well from start to finish, well over 24 hours at my end of the field. After the first few miles I put on a long-sleeved teeshirt and a light fleece under my waterproof and was comfortable to the end. A lot of people that day pulled out with near hypothermia  -  my contention would be that they simply were not wearing enough layers. Remember, when you can't generate enough heat to balance what's going on outside when in your normal running gear, you need insulation to slow down the heat loss - you have to take away the sensation of touching the inside of a cold wet outer layer. In fact, I suspect that's why we often believe a heavier weight "mountain jacket" with a light mesh lining is more waterproof than a lightweight running top - it isn't actually more waterproof but it offers more insulation and a cosier inside feel, it doesn't feel so "wet" inside so we think it's more waterproof.

4. Don't stop

I don't mean don't stop for the odd cup of tea or jam sandwich, but you have to realise that unless you can stop in a warm place, you really change the heat balance dramatically by stopping. You'll lose a lot of heat and start shivering fairly quickly, so get going again and get the balance back before you lose it completely. In the re-routed 2010 UTMB conditions were fairly wet and I was with two other UK guys most of the way through the Swiss section. We were all feeling pretty comfortable until one of the others stopped for a comfort break at the Bovine Alp checkpoint. Although it was no more than five minutes, the two of us left waiting were reduced to shivering and jumping on the spot to keep warm, and it took us several miles to get back to feeling comfortable again. I'm sure we've all had the experience where we finish a fairly damp event, spend a half hour or so at the finish if it's inside, chatting, drinking, lazing around, then find that after the hundred yard walk back to the car we're shivering almost too much to get the door open. And if you have no choice but to stop during an event in these conditions, because of an accident or similar, well that's the time to get out the spare DRY top that you've been carrying in the bottom of your bag to put on underneath everything else on just such an occasion!

Wet outings where you get cold can turn into varying degrees of misery. Wet events where you manage your temperature and are comfortable can be strangely satisfying, maybe even enjoyable. As Brits, we ought to be able to manage a bit of rain  -  we get plenty of practice.

No, your jacket doesn't leak.