Sources Of Humidity / Condensation

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Home Forums Campfire Editor’s Roundtable Sources Of Humidity / Condensation

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    John “Jay” Menna
    BPL Member


    Locale: 30.3668397,-97.7399123

    I really enjoyed Ryans podcast topic this week.  The idea of add a water tolerant top layer to a down sleeping bag system was something I had not thought about.

    But this made me think.  Is there any real hard data out there about the source of the humidity/condensation?

    Is it from humidity in the air?  Off my body or my breath?  By what percentage?

    By chance I was sleeping in the back of the Jeep, waiting for the snow to stop falling before I set out on a trail when I was listening to the podcast.  The inside of  jeeps windows were dripping wet by morning.  I have never had the inside of a vehicle get dripping wet when I was not (sleeping) in it.  That leads me to believe that the source of the bulk of moisture is me.

    Of that I am pretty sure that most of come out of my lungs and mouth.  Is the humidity creeping out of my sweat glands thru the down only to get condensed on the outside of the sleeping bag?  The fabric does not seem saturated.  It seems to be on the outside surface, not the inside surface.  Ryans extra layer on top is definitely a great idea in extended cold/wet trips no matter if the source is 2% sweat/ 98% breath or 50% sweat /50% breath.

    This all lead 8 hours on trail thinking (perhaps overthinking) about water inside my tent.

    If it is in fact from the mouth and nose,  wouldn’t it be possible to use a gossamer thin layer of fabric as a curtain to contain the flow of the and and thus moisture inside the tent?

    I guess Im asking.  Is the data out there already, or do I have to spend a lot of nights in the back yard to figure it out?

    David Thomas
    BPL Member


    Locale: North Woods. Far North.

    I’ve long pondered wearing a mouthpiece like a snorkel has, connected to check valves that allow exhalations to blow outside of the tent while inhalations would come from within the tent.  But that’s weight and bother and doesn’t eliminate body sweat so you still have some condensation.

    BC Bob
    BPL Member


    Locale: Vancouver Island

    Some mornings in the mountains, I wake up and the tent fly is bone dry, inside and out.  And the ground around the tent is dry.  Other mornings, the fly is dripping wet inside and out, and the ground is wet as well.

    So, IMO, assuming some decent ventilation in the tent, a wet fly mostly results from the overnight temperature dropping down to the dew point and moisture condensing on cold surfaces.

    Jerry Adams
    BPL Member


    Locale: Oregon and Washington

    if it’s clear the tent can cool to below the dew point and get lots of condensation

    another reason would be if there’s cold rain, then the tent fabric can cool to below the dew point and get lots of condensation

    I’ve experienced both of those

    Todd T
    BPL Member


    Locale: Pacific Northwest

    Body, breath, vegetation, wet ground, humid air, even combustion if you burn a candle or a stove.  You can eliminate the combustion, usually the vegetation, sometimes the wet ground, but the rest is generally uncontrollable.  Ventilate, set up under forest canopy, and live with the rest.

    BPL Member


    Locale: Northern California

    I think warm moisture from our breath is definitely one cause. But, like others, I can predict when condensation is going to occur in many scenarios, due to the environment (being in a valley with a river nearby, and cold air settling, for example.) since in most cases my breath alone, plus sweat, isn’t enough to cause condensation on my fly, I suppose these last are somewhat incidental after all.

    Brad Rogers
    BPL Member


    Locale: Southeast Tennessee

    <p>I live in the Southeast – high humidity is the norm.   Camp under tree cover (usually you don’t have a choice), avoid camping near streams, creeks, or rivers, and ventilation is key.  In the end though, even out west, when the conditions are right for condensation, you’re going to get some condensation.  </p><p>I remember a trip in January some years ago on the Appalachian Trail where I had ice all over the mesh in my inner tent.   24*F, thick as soup fog, no wind.   </p><p> </p>

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