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I've had a mummy style sleeping bag, with 100% Dacron polyester fill, for the better part of 20 years. The comfort rating is -5 degrees F. I hadn't used it in approximately 10 years. When I used it earlier this year it got down to around 35 degrees F and I was extremely cold whereas I had never been cold at this temperature, or colder, in this bag before. I understand that as we age our physiology changes and we can get cold easier, however what I'm wondering is if it's possible for a sleeping bag to lose some of it's insulation benefits with time? I've found a lot of information regarding temperature ratings and how an individuals physiology needs to be taken into consideration, but I'm having a hard time finding any information on how the comfort rating of the bag itself can change with time.

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You can generally assume that sleeping bags will lose some of their loft/insulating effect over time, which essentially boils down to a decrease of their capability to keep you warm - thus increasing the comfort temperature level. (Meaning that you'll only be comfortable to a not-as-cold-as-before temperature.)

Loft is affected by:

  • Compression, especially over longer periods.

    • Always store your sleeping bag uncompressed between trips.
    • When packing, don't roll or fold your sleeping back, but stuff it in somewhat 'randomly'. This prevents creases to appear, where the same filling material is compressed over and over again, thus damaging it.
  • Wetness/Moisture

    • Keep your bag dry, air it out frequently (in dry conditions).
    • Don't wash it unless absolutely needed.

Generally down sleeping bags are affected worse by this than synthetic fillings (that's what I was always told at my local store), but the upside is that down still is by far the best insulator, meaning lighter and smaller bags for the same insulation/comfort.

  • Yes, the comfort temperature level would increase. I'll make the appropriate edit to the title. – wanderweeer May 17 '18 at 10:27
  • As to washing: I have heard both: Some suggest that washing it with proper "soap" and drying it as recommended every X (?) used nights is beneficial, as it helps preventing the filling from sticking together. Others say never do it - I don't know the definite answer (if there even is one). – imsodin May 17 '18 at 10:27
  • @imsodin: I've heard both also. In favor of washing - it may possibly have something to do with dirt, and possible oils from ones skin, making the fill stick together therefore decreasing loft? I've only ever washed mine when the smell of campfire smoke was too overwhelming. – wanderweeer May 17 '18 at 10:38
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Yes a bag will lose loft with time. Loft = insulation. Your best bet is to store in a large bag or hanging in a cool dry place.

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