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When is a Hiking Rain Jacket like a Wet Suit?

Rain Jackets don't keep you dry in sustained rain, but they do help you stay warm.
Rain Jackets don’t keep you dry in sustained rain, but they do help you stay warm.

Hiking rain jackets don’t keep you dry in the rain; they keep you warm. If you don’t believe me, go hiking in the rain for 4+ hours and see if the clothing inside your jacket stays dry. Unless you’re hiking someplace with extremely low humidity, I bet the clothing under your jacket will get wet, if not soaked-through by sweat and condensation. Like so-called waterproof hiking boots, hiking rain jackets are another item of hiking gear where the expectations don’t match the results.

Wetsuits haven't changed much since the 70's and still work by insulating a thin film of water near your body.
Wetsuits haven’t changed much since the 70’s and still work by insulating a thin film of water near your body.

Which is why, you should think of a hiking rain jacket as a wet suit that will keep you warm when you’re wet, instead of preventing you from getting wet.

How Wet Suits Work

Wet suits are not meant to keep you entirely dry. Instead, they trap a thin layer of water between your body and the suit. This layer of water is warmed by your body, to prevent you from loosing too much heat while in the water.

Wet suits are made of neoprene, which is made of small closed cells that are filled with air and provide insulation against cold water by trapping heat in.

How to Make Your Rain Jacket Work Like a Wet Suit

The key to making your rain jacket work like a wet suit depends on what mid-layer insulation you wear. Since rain jackets are only like an outer skin, you’re going to want to wear a mid-layer that can trap air that you can warm with your body heat, but that won’t be compromised by the condensation that occurs on the inside of your jacket when it begins to rain.

The best mid-layers for this purpose are fleece or wool pullovers, worn over a synthetic or wool baselayer. Fleece is a hydrophobic material, holding less than 1% of its weight in water and retains much of its insulating powers even when wet. It also dries much faster than wool. While Wool also retains warmth when wet, it absorbs up to 30% of its weight in water and takes longer to dry.

Whatever you do. Don’t wear cotton, hemp, bamboo, or other garments made with plant-based fibers as mid-layer and base-layer garments under a rain jacket. These materials soak up so much water that they can’t retain warm air. The water fills up all of the air spaces in the fabric and your body can’t generate enough warmth to warm it up.


What Good is a Rain Jacket Then?

Why bother with a rain jacket if it just makes your mid-layer wet in rain from condensation or by trapping your sweat? Good question.

Rain shells, like house wrap, trap heat when worn so it doesn’t escape. They also help prevent something called evaporative cooling, which occurs when wind or air comes in contact with your torso and legs and causes evaporation to occur. Evaporation sucks heat out of your body – which is why the process of sweating cools you.

You can break the “evaporative chain” by wearing an insulating mid-layer like a fleece pullover, which preserves the air space around your body, and keeps the thin-film of wetness (caused by condensation) between its outer surface and inside of your rain jacket.

While the combination of an insulating mid-layer and rain jacket doesn’t work exactly the same way as a wet suit, the underlying principles are quite similar. Your body heats the air trapped by your mid-layer, while your rain jacket keeps the resulting warmth from escaping.

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  1. The two possible solutions to this are two brands which I don’t think travel overseas very well. First is Buffalo systems which are not designed to be waterproof but which are vey good at managing condensation and keeping you warm in cool/cold damp conditions. Second is Paramo – very unfashionable but very good (IMHO) at managing condensation and keeping out the rain. Both use fundamentally different design principles to the convention hard-shell breathable construction. Both are probably best described as soft-shell philosophy. I use and really like both brands – and I “run hot” and sweat a lot. But at the end of a full day in the rain you will be very lucky to be completely dry – cope with it.

    • +1 on Buffalo Systems equipment. I use my Special 6 winter hiking in the Whites. Pile and Pertex garments do work very well when it’s cold, wet, and windy.

  2. Hmmmm…

    I see the points but at the same time it us also dependent upon one’s level of exertion.

    As you may be aware I have had some experience with epic soakers.

    One that comes to mind is a 12 day solo where the state set records for rainfall (11 days it poured nonstop.)

    During this trip I utilized my Westcomb Specter and in all honesty I was in fact completely dry.

    When wearing rainwear I slow my pace.
    I believe this had a bit to do with it.

    Also body chemistry will play a big part in this.

    Nevertheless, just wanted to offer some thoughts from my end on this subject.

    Good subject.

    -Loco Raindrops

  3. A minor point about wetsuits, they HAVE changed radically since the seventies. In fact over the past few years they have become much warmer, lighter, flexible and more comfortable with invention of superstretch neoprene.

    I would never wear a wetsuit hiking unless I was going to hike through rivers in cold weather, but when it comes to watersports, I have found the newer surf wetsuits can replace a drysuit in all but the coldest water/weather.

  4. Ah, so it’s Mythbusting Week on Sectionhiker.com, is it? :-)

  5. What base layer/mid layer traps air better than any other? Brynje mesh base layers. Full disclosure, I sell it in the UK and to the US, but in this situation, I would be very surprised if anything works better.

  6. Chouinard Equipment used to make a foam rain coat and pants that would work nicely in this context. For some reason it never caught on like his crazy fleece idea did.

  7. One other way the rain jacket helps – it prevents cold rain from making contact with you and directly carrying away your body heat. That’s a slightly different wrinkle on it “trapping heat so it can’t escape”, i.e. blocking diffusion to the surrounding air. I agree that the fleece mid-layer is key.

  8. You have to consider the pack you have on your back – which covers the greatest area of possible moisture transfer.

    I’m sure manufacturers don’t take the pack into account so real world usage of a jacket with pack on may yield quite different results.

  9. Sorry Philip, my base layer and shirt often dry under a rain jacket (while it is raining), even if they were wet when I put the rain jacket on (a 20 year old Gore-Tex). While I don’t contend it works for everyone, I find it the best way to dry clothes for me.

  10. I’d love to meet all of you folks who don’t sweat under their rain gear. See how you do it. 5 minutes in a rain jacket and I’m sweating like crazy.

  11. I grew up and started hiking in the Pacific NW, and have lived in Southcentral Alaska for the last 30 years, so I have hiked in the rain once or twice. If it is fairly warm out, I often don’t put on my rain jacket at all. I just wear a light shirt and get wet. My insulation and rain jacket stay dry in my pack. When I stop I strip off the wet shirt, and put on a dry layer and my rain jacket. In chillier temperatures and/or strong winds, I usually still just wear a light shirt but will put my jacket on over it. I don’t wear much insulation when moving, unless it is bitterly cold. I like good pit-zips in my jackets. Also a hat with a brim to keep the rain off of my glasses.

    I’m getting to be an old geezer, but I tend to get pretty warm when I’m hiking or skiing. Even in the winter, I find that if I’m dressed so that I’m about freezing to death when I’m standing around at the trailhead, then I’ll be about right once I get moving. Since the climate in these parts can be highly variable and severe at times, I always carry a lot of warm clothes, but often they stay in my pack except when I stop.

  12. Rain jackets are for camping to keep your dry clothes dry after you hike.Unless you wore it and already wet it out.
    Wool thin long sleeve shirt and a backpacking umbrella and a kilt with shorts is what should be worn hiking/backpacking .
    Jacket is to keep from getting cold only if you have it on while backpacking/hiking.

  13. I usually wear a heavy poncho in the summer and stay mostly dry. Maybe because the bottom is so open it allows my body to breathe better? I use the shell jacket for cold rain, snow and sleet.

  14. I also like ponchos, except on top of a mountain where it might act like a sail and get me blown off a cliff. Mine is an inexpensive but thick plastic version. If it tears, it only cost $1.50, so I don’t care. It breathes well from the sides, covers my pack, and I can hold the edges and my hiking poles at the same time, thus keeping my hands dry too. Imput my tilley style hat on top of the hood to anchorbit in a position that does not hamper my vision yet keeps the back of my head and neck dry. My heavy gortex jacket is now for walking to work in cool weather.

  15. There are better ways to manage moisture under a rain jacket than resigning to using it like a wetsuit. This article implies that you SHOULD treat the system like a wetsuit, rather than teaching how to manage moisture, lower exertion, use venting, etc. I understand that you’ll be warm(er) with a rain jacket and a wet/damp midlayer than with no rain jacket, but that is precisely what causes hypothermia and death when conditions aren’t ideal. No company makes rain jackets with the idea that they’ll be used in the way you put forth in this article, Philip.

    • Nope, I’m just saying that when your waterproof layer doesn’t live up to your expectations (for whatever reason), you should put on a mid-layer to retain warmth. That’s really not controversial.

  16. Would someone care to wax poetically about zip-pits? I would rather be cooler than clammy, I try to find a balance.

  17. If I get cold in camp, I often put on a rain jacket or pants to hold in heat.

  18. In your opinion, during light (intermittent) rain is it better just to use fleece? It seems like if you are moving at a pretty good pace, it might make some sense.

    • I like to keep my upper layers as dry as possible, so I’d probably opt to wear a rain shell over the fleece or just the rain shell. I’m far less concerned about my legs getting wet in rain and only put on rain pants if I start to get chilled. My legs generate a lot of heat since they’re doing most of the work.

  19. 90% of the time:

    Baselayer and windshirt in the summer
    fleece and windshirt in the cooler months

    Raincoat after I’ve changed and stopped for the day or when it’s really chucking it down

    I used to wear a “wetsuit” until my enlightenment.

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