3 season sleeping bag system: how best to deal with interior moisture?

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    Bryan Redd


    What are the “best” ways to deal with interior moisture (from insensible perspiration and actual persperation) and salts from persperation while in a sleeping bag during moderate >25 degrees <60 degress 3-season camping? In other words, what performs best to prevent moisture and salt degradation of the sleeping bag's insulation over a multi-day trip in these conditions? Also, to avoid the weight build up in the bag's insulation which reportedly occurs over a period of days as the interior moisture and salts get into the insulation.

    1. Clothing on while sleeping (e.g. fine merino wool long underwear or a synthetic alternative).?

    2. Sleeping bag liner such as a silk liner, with less or no clothing on while sleeping (depending on temperature)?

    3. Other solutions?

    Matt Gordon


    Just an idea I read somewhere…

    Wear your rain jacket / outer shell in the bag at night. Put it next to your skin or wear your thinnest layer in between you and the rain gear. While this isn’t a true vapor barrier, it should cut down on a significant portion of your body moisture (hopefully you haven’t invested in the high end wp/br materials).

    If this isn’t effective, you can always try a true vapor barrier liner in your bag, or vb clothing.

    Bryan Redd


    In light of the moderate temps of most of my 3-season backpacking, a true vapor barrier doesn’t work—too warm, creating too much moisture within the barrier.

    So, what are some good alternatives to a vapor barrier, that will reduce the amount of moisture/salts accumulation in the bag’s insulation, but will not cause overheating and extensive moisture/wetness next to skin?

    A silk bag liner? Thin merino wool layer clothing? Other?

    Ken Helwig
    BPL Member


    Locale: Scotts Valley CA via San Jose, CA

    Hi I have used both vapor barriers and liners. For me I really don’t like bringing something extra like those two when I could double up my clothing as part of my sleep system. By using smartwool for you next to skin and a good primaloft jacket I can stay warmer and not have the added weight. Most of your sweat when you sleep will stay with your clothes and won’t affect your bag too much. The up side to that is both of the pieces of clothing I mentioned could be dried pretty quickly in the new day sun.

    dan kutcher


    I’m of the same opinion as the previous poster. I try not to carry anything that can’t serve a dual purpose. For that reason, I wear the thinnest synthetic long handled underwear I own as sleep wear. That way, I can wear it around camp in the morning while I air my bag and make breakfast. By wearing it only to bed after wiping some loose grime from myself, and cleaning the nether regions, I have something I can wear into town, if necessary (the bottoms being worn under shorts, of course).
    Since you asked for solutions regarding three season hiking, I would not suggest using a vapor barrier. They tend to make you overheat and sweat in temps. over 25F or so. Also, anything you wear inside a vapor barrier gets very damp, so don’t wear insulating layers in one if you use one in the winter.

    Richard Nelridge


    Locale: Eastern Pennsylvania

    Particularly in temperatures of about 32 degrees F and lower you can wear a Vapor Barrier Shirt and Pants. These will take the place of much of your thermals (or other clothing when sleeping); you would have to experiment regarding your metabolism to find what works. With the Vapor Barrier clothing you keep the moisture next to your skin. Thereby you can can wear other clothing outside the Vapor Barrier Clothing, but inside the sleeping bag without fear of wetting out your clothing or your sleeping bag insulation. In the process you can carry a lighter sleeping bag because the vapor Barrier Clothing will give the equivalent to an additional 10 to 15 degrees F of insulation. My Stephenson’s Warmlite ( Vapor Barrier Top and Pants together weigh about 9.8 oz.

    Edward Ripley-Duggan


    I agree with Richard that this is far and away the most flexible and utilitarian sleep/day system, preferable IMO to VB sleeping bags and liners. Since feet tend to get cold, VB socks are also a good idea. All VB clothing needs a little experimentation to use optimally. The Stephenson shirt is great, but if you are using it during the day, you will tend to find that fairly minimal layering is needed on quite cold days. Despite the temptation to cut ounces, I’d say a little redundancy, both in bag weight and layers, is a good thing until you are absolutely confident what your comfort and safety margins are.

    For cooler three season nights, a windshirt e.g. the Chinook is great and multi-function. True VB is strictly a cold-temperature technology.

    At a pinch, plastic bags make great vapor barriers. I use painter’s gloves ($3/100) both as a hand VB layer and in my First Aid kit (though a pair of serious latex gloves is a good thing for the latter if there’s any issue with blood-borne pathogens).


    Matt Gordon


    Has anyone ever had a bag (or clothing) with the wp/br material on the inside and a more breathable material as the outer shell?

    This would cut down on moisture being absorbed into the lining from your body, and still allow the outside to breathe / dry out during the night or the next day.

    Feel free to shoot this one down, since it just popped into my head and I haven’t really thought it through. Just an idea.

    Michael Martin
    BPL Member


    Locale: North Idaho

    > Has anyone ever had a bag (or clothing) with the wp/br material on the inside and a more breathable material as the outer shell?

    Sounds like a great idea! I’d like to see *reversible* jackets and bags w/ eVent or Pertex Endurance on one side and quantum on the other. In wet conditions, wear the wp/b side out; in dry conditions wear the quantum side out, where the wp/b fabric would reduce additional moisture accumulation and allow body heat to dry the insulation through the quantum.

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