Jackets with Pit Zips: When Are They Effective?

Jacket Pit Zips - When are they Effective?

Jacket pit zips are zippered openings located under the armpits on many rain jackets and winter shells. They’re designed to help you vent excess body heat, so you perspire less when wearing waterproof/breathable or non-breathable jackets. Pit zips are positioned in your armpits because your arms and shoulders shield them from rain. Major blood vessels also pass close to your armpits, providing an efficient way to shed excess body heat when exposed to colder temperatures.

Perspiration and Condensation

When you wear a rain jacket or winter shell and zip it up, it’s going to insulate you by trapping your body heat. When body heat has no place to go and the temperature inside your jacket exceeds the temperature outside, you’ll start to perspire, which is the body’s way of venting excess heat. You’re also likely to experience condensation when water vapor inside your jacket comes in contact with the inside surface of the external fabric, which is cooled by the outside air. Perspiration and condensation are the two ways that you can feel wet inside a rain jacket or winter shell (See: Why Do I Get Wet Inside My Rain Jacket).

The Enlightened Equipment Visp Rain Jacket comes with 11” pit zips
The Enlightened Equipment Visp Rain Jacket comes with 11” pit zips

But if you open your pit zips, you can shed some of that excess body heat and avoid or reduce the degree of perspiration you experience. The trick is to do it when you begin to feel warm, rather than waiting until you feel wet with sweat. Some people just keep their pit zips open all the time, even if they feel a little cool when they start hiking and before their body heats up.

Pit zips are most effective when there is a large temperature differential between the inside of your jacket and the outside world. Depending on where you hike, this will occur when temperatures are cooler in spring, winter, and autumn. But pit zips are unlikely to provide much relief in summer when the temperature inside your jacket is close to the temperature outside.

Comparison Table

Make / ModelPit ZipsAvg WeightPrice
Marmot Precip ECOYes10.9 oz$100
Black Diamond Stormline StretchYes9.9 oz$149
Outdoor Research HeliumNo6.3 oz$159
Enlightened Equipment VispYes5.3 oz$200
Outdoor Research Foray JacketYes16.3 oz$215
Montbell Versalite JacketYes6.4 oz$200
REI DryPointNo10.5 oz$249
REI StormboltYes14.6 oz$279
Zpacks VerticeYes6.2 oz$259
Marmot BantamweightNo5 oz$275
Montbell Storm CruiserYes10 oz$299
ArcTeryx Zeta SLNo10.9 oz$299
Lightheart Gear Silpoly Rain JacketYes6.7 oz$115
Frogg Toggs XTreme Light JacketNo10.3 oz$55
REI Rainier JacketYes11.4 oz$90
Patagonia Torrentshell 3LYes13.9 oz$149

Jackets without Pit Zips

Some rain jacket and winter shell manufacturers don’t put pit zips into their jackets at all, instead relying on waterproof/breathable membranes to vent water vapor before it condenses into liquid form. It’s important to understand that these membranes can only vent water vapor, not perspiration or condensate. When your skin feels wet, it’s too late for your waterproof/breathable jacket to provide much relief…unless it can boil off the liquid and turn in into vapor again which would require a lot of energy.

The Outdoor Research Foray Jacket has torso zips that run from the armpits to the waist for maximum temperature regulation.
The Outdoor Research Foray Jacket has torso zips that run from the armpits to the waist for maximum temperature regulation.

Why don’t manufacturers always put pit zips in rain jackets? It’s hard to give a definitive answer, so here are a few possible reasons.

  • Adding pit zips increases the cost of manufacture and results in reduced profitability.
  • Adding pit zips to a waterproof breathable/jacket diminishes the value of the breathable membrane.
  • Adding pit zips adds extra weight to a jacket.
  • Gore-tex prohibits us from putting pit zips in rain jackets that use their breathable membrane.
  • People will still buy a jacket that doesn’t have pit zips if we tell them it defies the laws of physics.

Limitations of Pit Zips

Despite their benefits, pit zips have their limitations, especially in hot and humid weather when it’s impossible to shed body heat if you have to wear a rain jacket. If there isn’t the potential for hypothermia, which can occur even in summer, you’re probably better off using an umbrella, which is like an UBER pit zip for shedding body heat, while keeping your torso dry.

But in conditions where there is a decent temperature differential between the warmth inside your jacket and exterior coolness, the bigger your pit zips, the better. For example, both the Montbell Versalite Jacket and the new Lightheart Gear Silpoly Rain Jacket have 18″ long pits zips, which are definitely on the long side. Some manufacturers like Outdoor Research even put torso zips on their jackets which run from the biceps down to the waist. The ones on the OR Foray Jacket, for example, are particularly effective. Even if pit zips don’t completely eliminate heat build-up inside a rain jacket or shell, they’re better than not having them at all.

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17 comments

  1. For many years I’ve read that GoreTex REQUIRES pit zips. Has something changed?

  2. I have the OR Foray here in the PNW, and I heartily agree!

  3. Do you think pit zips jackets are better than the normal hiking jackets ?

    • I’m not sure what a “normal” hiking jacket is. There are rain jackets, wind shirts, winter shells, soft shell jackets, lightweight insulated jackets and hoodies, etc. When rain is involved I far prefer jackets with pit zips. You have to understand that most jackets are not deliberately designed for hikers.

  4. What’s your go-to rain jacket, when you’re not reviewing? I’ve been using the LightHeart Gear jacket, which has served me well. On a recent backpack, my buddy and I did a lot of hiking in the rain. I got wet from perspiration, despite the pit zips, but kept warm. And when we got to camp, I wiped down the inside with a face cloth. Since the jacket cannot absorb water, it was ready to put on as a layer, if needed.

    • Hunting season started yesterday so I’ve switched to my blaze orange silpoly Lightheart Gear rain jacket. Used it yesterday as I hiked up Wildcat D via the ski trail which is close to a bushwhack in places. Heard gunshots. For three season I use a Montbell Versalite. For winter, I’m currently using an REI Drypoint GTX or a Sitka 3L Dewpoint.

  5. I had what I think was the first Goretex jacket w pit zips, back in 1979. Made by a company named Synergy Works. Loved the pit zips, but the Goretex sucked back then. Fast forward to now. Loved the airyness of the OR Foray, basically a poncho w sleeves. But it was heavy and had some other issues like leaky neck seam where we all sweat. Now use a Montbell Versalite, under 7 oz. Here in N GA, pit zips are great in shoulder season rain w temps in 40s. If Im not producing sweat uphill, my shirt (Smartwool) will start drying except under rhe pack. Nice to see some UL companies going to longer zips at minimal weight gain.

  6. Do ponchos have a place in your usage between a rain jacket an and umbrella? Or are their negatives in wind and underbrush so similar to umbrella negatives that you skip the poncho option?

  7. When, back in the late ’80s, I saw my first pit zip in a mountain parka I imediatelyhad our local tailor shop install pit zips in 3 outdoor jackets. I know from long experience EXACTLY when to use them – mainly during strenuous exercise but at the beginning, before I get heated up.

    Bit if you’re doing moderate exercise in the rain just leave them closed to force your WPB membrane to so its work – int that is the fabric which the zips are installed.

  8. I purchased a Lightheart Gear Rain jacket last year after reading your review. Really pleased with the jacket and the ventilation the pit zips provide along with a material that won’t wet out.

  9. Pack straps pretty much hold the vents closed so they are much less effective when wearing a pack.

    Pit Zips are excellent for for cross-country skiing, snow shoeing, or day hiking with trekking poles (without a pack) where the motion of arms reaching up to grasp the poles gives a bellows effect to eject moisture-laden air out through the pit zips. These are pretty much high exertion activities, so the pits zips help.

    Pit zips with rain flaps to protect the zipper are an oxymoron. If they have Velcro to hold the flaps closed, this keeps the slits from opening. I removed the the Velcro tab on one side of each pit zip. (Use seam sealer over the thread holes if you do this.)

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