Why do I get wet inside my rain jacket?

Why do I get wet inside my rain jacket?

The leading causes of wetness inside your rain jacket are condensation and perspiration. Condensation occurs water vapor encounters a colder surface and changes from a gaseous form into a liquid one. When the air is humid it has a lot of water vapor in it. If the external surface of your rain jacket is cooler than its interior, the water vapor will condense on the inside your jacket and make your clothes wet.

Perspiration also produces water vapor and condenses by the same process. You can reduce the amount you perspire when wearing a rain jacket by taking off clothing layers worn underneath it or by generating less body heat, by being less active. For example, mountain climbers deliberately slow down their pace to reduce the amount they sweat so they don’t soak their insulation and reduce its effectiveness.

Pit Zips

A rain jacket acts as a thermal envelope and makes you warmer by trapping body heat. If your rain jacket has pit zips, you can open them to shed some of the warmth so you perspire less. You can do this without getting wet from the rain because your arms cover the pit zips and prevent rainwater from dripping into them. It’s not perfect, but it can reduce the amount of water vapor that’s produced when you sweat, thereby reducing the amount of condensation that makes your clothes wet.

Wearing a rain hat instead of using a jacket’s hood is another way to vent excess body heat since your blood flows close to the skin in your neck where it can be cooled by the surrounding air. If you don’t mind getting your hands and wrists wet, you can also push up your arm sleeves, because there’s also a lot of blood flowing near the surface of your wrists.

If you have a rain jacket that doesn’t have pit zips, there’s really no way to reduce the amount of heat trapped inside your jacket without stopping and shedding clothing layers. Unfortunately, that’s often not practical if its pouring rain.

Waterproof/Breathable Rain Jackets

Waterproof/breathable jackets are designed to release the water vapor that accumulates inside your jacket when you zip it closed. These jackets have a breathable layer with microscopic pores that vent water vapor while preventing rain drops from entering. They only release water vapor in its gaseous form, however, so you’re stuck with any liquid condensation that’s already formed inside your jacket.

A waterproof/breathable jacket is made with several different fabrics and materials that are sandwiched together. A  waterproof/breathable layer is often sandwiched between other fabrics or materials that protect it since its very thin and delicate. It’s important that these remain clean and don’t obstruct the passage of water vapor through the waterproof/breathable layer. This requires frequent washing and treating the exterior surface of the jacket with a chemical coating called DWR, which stands for durable water repellent.

The DWR coating makes rain bead up and run off the exterior of the jacket. If the DWR coating wears off, then a jacket’s outer fabric can get saturated, blocking the waterproof/breathable layer’s microscopic pores. The waterproof/breathable layer will still prevent water from penetrating deeper into the jacket to make you wet, but the soaked outer fabric will prevent water vapor transmission. With nowhere to go, the water vapor will condense and makes your clothing wet.

Unfortunately, the DWR coating deteriorates a little every time you use the jacket, fold it up, or stuff it into your backpack. While you can reproof it occasionally with a product like NikWax TX Direct, the DWR will never be as effective as the day you bought it.

If you own a waterproof/breathable jacket and your DWR coating fails, having a rain jacket with pit zips will at least let you dump excess heat, resulting in less perspiration, and less condensation.

Summary

Condensation and perspiration are the primary reasons that you can get wet inside a raincoat. Condensation occurs when water vapor touches a colder surface, like the inside of your rain jacket which acts as a thermal envelope keeping colder external air from chilling you. You can reduce the amount of water vapor inside your jacket and the amount you perspire by opening pit zips which are designed to cool you off. While waterproof/breathable jackets can vent water vapor, they can only vent it in its gaseous form and not after it’s condensed into a liquid. The DWR coating on most waterproof/breathable jackets must be carefully maintained and reproofed to maintain a jacket’s breathability performance.

If you don’t have a rain jacket with pit zips, you should consider getting one. Some waterproof/breathable jacket manufacturers also include pit zips in their jackets because there’s no other way to release the body heat (when it’s raining) that leads to increased perspiration.

Here are a few popular examples:

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33 comments

  1. Great write. It helps to have an experienced and well thought explanation. It is hard to figure out whats wrong while reading the standard publications of the gear companies and unfortunately individuals repeat those uncritically.
    According to this article isn’t it best to have a non breathable waterproof jacket rather than the breathable ones?

    • I think that the decision to make is somewhat different – should you buy a jacket with pit zips or not?

      All rain jackets, breathable (and there are many different levels of breathability) or not suffer from condensation. That’s a law of nature like gravity. You can reduce the level of condensation by cooling yourself off with pit zips.

      In my experience, breathable jackets are higher quality than non-breathable ones, with better zippers, adjustable hoods, and taped seams. They’re also far more abundant in terms of choice. But they require considerable extra DWR and washing to maintain the breathability. Most people aren’t willing to take the time to do this. If you’re not willing to do it, buying an expensive breathable jacket is pointless.

      Even if you do maintain the DWR, breathable jackets are still not immune to condensation because they can’t keep up with the amount of water vapor in the air or that you perspire. Pit zips are the best way to dump extra heat, but they won’t let you dump all your extra body heat and you’re still likely to get damp inside your jacket, especially if you’re a hiker wearing a backpack. Skiers riding up chair lifts don’t sweat as much….

      There’s also the issue of fabric thickness which isn’t often talked about. Heavier jackets with thicker fabric insulate more so you sweat more.

      Ultimately, this all comes down to cost. if you buy a non-breathable rain jacket, you want one with pit zips. If you buy a breathable rain jacket you’re going to want one with pitzips. You simply cannot rely on breathability as the only means of venting all the water vapor in the air or that you create (through perspiration) inside a rain jacket.

      Is that clearer?

      The harsh reality is that you’re probably going to get damp inside with any rain jacket. The bigger issue is maintaining a comfortable level of warmth and pitzips provide a better option for self-regulating that than none at all.

      • Thanks for the elaborated and helpful. I’m definitely lazy enough to buy the non breathable ones.

      • I would love to know exactly what percentage of my perspiration actually exits through the “breathable” membrane. I, and most all of my outdoor partners, find that any jacket, mo matter how expensive or well-constructed, is mostly a perspiration barrier during even moderate exercise.

        Now a days we just wear unshelled fleece as long as the wind and precipitation allows.

        And i won’t buy any shell without pit zips or thigh vents.

    • I tried a OR rain jacket with zips, still had a condensation problem, guess my body needs more ventilation. I use a rain skirt to keep my waist to knee areas dry. I use a hiking umbrella to keep my upper torso dry and use just one hiking pole. In super heavy rain I will add a super light weight rain jacket but I keep it unzip just to keep my back dry from when heavy rain has a habit of sliding between my back and backpack, but 90% of the time the umbrella works.

  2. Thoughts on the Packa, the hybrid cagoule/poncho/packcover, with the huge pit zips, and the long and open ventable bottom?
    Works well for me in my trials.

    • I’ve never tried one, but I imagine it would be annoying in the wind (think mountains) and cold (including winter), since it probably doesn’t hold your heat very well. Personally, I like a rain jacket with pockets, that’s also light enough to use as a wind shirt. I could see using a Packa in summer on a heavily forested trail maybe.

    • Great advice cheers

  3. I’ve had to move to using a poncho and, only when necessary, chaps as I’ve never been able to stay cool enough in any jacket, even with pit zips (I sweat A LOT). The problem is most ponchos don’t offer a zip up or button up front to allow excess heat and vapor to escape. I wish more manufacturers would incorporate this small change. Plus, the poncho works quadruples as a pack cover, ground sheet, and cooking/sleeping tarp.

    Years ago when they were pushing their cagoules, ponchos, and chaps, I thought I remembered Sierra Designs saying that mechanical venting (including pit zips) was 40% more effective than even the best waterproof breathable fabric. Do you remember anything along those lines?

    • Chad wrote: “…most ponchos don’t offer a zip up or button up front…”

      It’s a bit of work, but my wife has a cheap Frog Toggs poncho which she slit up the front and added snaps to. In the wind it’s like wearing a sail sometimes, but it’s definitely got an edge in terms of ventilation. I’ve been using an umbrella along with an unzipped non-breathable rain jacket when hiking, but eyeing her poncho has me thinking about switching out my unzipped jacket for her unbuttoned (or partially buttoned) poncho. The negative would be that I also use my rain jacket as a wind shell, which won’t really work with a poncho.

      But I guess my point is if you’ve got a sewing machine or know someone who does, gear mods can get you closer to what you really want or need perhaps.

  4. Do you know anything about the environmental impact of aftermarket DWR? That gives me pause to re-treating my old marmot precip

  5. I know that many people rate them but I have never found pit zips that useful.
    My arms normally force the opening closed when I walk.
    In the past i have found tjat if I periodically bellow the front of the jacket manually and have a loose cut jacket it expels hot air from the body much more effectively.
    I now have a columbia jacket with forward facing vents and external membrane (can’t wet out) that is a better solution IMHO.

  6. This is a good write up and clear explanation. I’ve tried all of the expensive jackets, and for a long time I was a die hard Arcteryx user. Over the last few years though, I’ve gone back to a basic silnylon jacket, for many of the reasons you mention.

    I hike hard, and build up heat in ALL of my rain jackets. The best way for me to regulate heat is via the front zipper and pit zips. I currently use a Light Heart jacket in warmer seasons, and a Marmot Precip in colder temperatures. I like the straighter style of the man’s Marmot Precip because I can layer it better over other clothes.

    I don’t need to pay the price of the “breathable” jackets when I get almost the same results from less expensive jackets like Light Heart or Frog Toggs.

  7. Philip, what is your current personal pick for 3-season rain jacket? If I remember correctly, you had been using the Lightheart Gear, non-breathable one listed above. Still your favorite?

  8. As you’ve said before, Phil, it’s unlikely that any rain jacket will keep you dry if you are exercising because “breathable” fabric simply can’t keep up with anything but lower levels of perspiration.

    I skin up a ski area every morning at “level 3 or 4” (of 5) work rate. I use a decision tree approach to clothing:

    1) Do I need a shell or not because of snow or wind?

    If not, then no matter what the temperature, I’ll layer with fleece that has as many zippers as possible (full front, pits, pockets…. many mfg have engineered pockets to be useful heat dumps. Any shell or wind stopper retains too much heat.

    If I do need a shell for wind, it’s plain nylon with no DWR or the like so that it’ll let some perspiration out and have limited condensation. I won’t wear a shell bottom and tough it out because it’s too warm unless totally unzipped sides, which defeats the purpose.

    If I need snow protection, it’ll have as many zippers as possible, and under layers will too, for temperature regulation. But I’ll expect to be soaked inside at the top even with various unzipping.

    In any case, I’ll be soaked at the top. If it’s not snowing, I’ll have a shell top and bottom in my pack to wear on the way down and have to rinse and dry my layers when I get home.

    I’d love to find a lighter weight softshell pant with full side zips, like an REI Activator that can vent. (BTW, thanks for that tip last year. And yes, you were right that they really are too warm for anything but very cold weather, hence the dream that they’d have vents!)

  9. A good discussion of the topic. Growing up in the Pacific Northwest, and having spent the last three decades in Alaska, I’ve done a bit of hiking in the rain. I’ve heard many people complain that their raingear was “leaking”, when in fact it is really perspiration and condensation accumulating against the inside of the jacket. “Breathable” fabrics help in dry windy weather but when the outside of the jacket is wet from rain, I doubt that much if any water vapor passes from the inside of the jacket through the breathable membrane.

    Pit zips help, as does unzipping as much as possible, opening the cuffs, etc. I tend to run hot, so if I feel like I’m freezing to death while fussing around at the trailhead, I’ll be about right when I get moving up the trail. So I tend to dress lightly but carry a good bit of extra clothing in my pack. In cold rainy weather and a steep uphill hike, I will sometimes only wear a lightweight smart wool base layer under my rain jacket. When I stop, I’ll quickly add another dry layer of pile or fleece under the rain jacket.

    • I’ve found that if I’m somewhat uncomfortably cold at the trailhead, I’ll be just fine after a quarter mile.

    • I have seen wetted out jackets with bubbles lots of times. The bubbles are the vapor passing out through the jacket. So it does happen just not as easily or as fast as when not wetted out.

  10. What product do you recommend to maintain breathability? is it just a delicate cycle on a front loading washing machine that’s best, with this product, that’s best ?

  11. Rosemary Szponarski

    What product do you recommend to maintain breathability? is it just a delicate cycle on a front loading washing machine that’s best, with this product, that’s best ?

  12. Any commentary on the breathability of woolen items and layers? versus cotton?

  13. I moved away from jackets with membranes as my main waterproof almost 7 years ago. No matter whether it was main brand membrane jackets or budget ones I eventually got wet from sweat. Even with pitzips. I moved to Paramo which use a totally different concept where sweat is pumped away from the body. I have worn my waterproofs in very heavy rain and humid conditions for hours without getting wet inside. The disadvantages of Paramo is that they are relatively heavy, are warmer than shells, and expensive. They work best if washed regularly. The waterproofs seem to be very durable compared to membrane based shells. My lest jacket is showing no signs of wear at 7 years of use. They also come with an excellent warranty from the company who regularly get plaudits for their ethical production.

    • I’ve tried them. Too hot for me.

    • I use Paramo a lot in winter. I find it best when not wearing a rucksack and when it is cold. I can’t think of anything better in those circumstances. The breathability and perspiration management are unsurpassed in my experience. Also, it is simply more comfortable than anything else. It is buttery soft against the skin or over layers. My experiences do not suggest it would be the wonder fabric suggested in days of rain wearing a rucksack. But to be fair I have never tried that.

  14. Just a thought: “The waterproof/breathable layer will still prevent water from penetrating deeper into the jacket to make you wet, but the soaked outer fabric will prevent water vapor transmission. With nowhere to go, the water vapor will condense and makes your clothing wet”

    As far as I know, most WPB layers rely on pretty much the exact same physical properties as DWR does – the minuscule pores in the membrane don’t work by being “smaller than water droplets” like the marketing crap says (a physical nonsense), but by being hydrophobic and relying on surface tension (normally, water would just seep right through into less saturated area, but a hydrophobic membrane makes all water into large droplets that can’t get through that easily). If you lose that membrane’s hydrophobicity (through dirt, soap, sweat and other hydrophilic substances), it doesn’t work anymore. Plus, pushing water vapour outside requires a temperature or saturation gradient. If there is none, membranes don’t work much either, especially if cold on both sides. That’s why GTX and others don’t work much if the outer is saturated by rain.

  15. I find that what keeps my clothes driest while hiking in a significant rain is a fully unzipped rainjacket plus an umbrella, +/- rainpants depending on whether I’m in pants or shorts.

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