This is a preview of a member exclusive premium article.

There is a lot of literature on how to stay warm doing outdoor activities. But I am not satisfied because most of the information about heat loss is qualitative, anecdotal, or based on some ancient source; thus I have tried to better measure heat loss.

I wrote an article about

  • Roger Caffin's article on measuring insulation values of sleeping mats.
  • Richard Nisely's Thread.:
  • Richard Nisely's Thread.
  • Another good internet source is this Mammut article.
  • Some other interesting links I used for this article:

    Thanks to Roger for reviewing this article and giving me a bunch of ideas.

    Like my previous article, there are limits to what you can do with home-made instrumentation. To do this properly you need to use expensive lab equipment certified by some standards laboratory, which I don't have. Thus, there is uncertainty about my results, but this at least raises some questions that I think are interesting. There is both geeky analysis and practical information.

    Also I am conducting my testing outside on my patio. If I was in an environmentally controlled lab I would get more consistent results since there are uncontrolled variables on my patio. For example, the wind varies during testing so all the variables are not always consistent and the results are less repeatable. I can largely eliminate this by, for example, repeating measurements and making sure I get the same result. On the other hand, my patio is actually much closer to the actual conditions I sleep in so my results are more useful.

    My main interest is how to stay warm enough when I'm (trying to) sleep at night. Usually the temperature gradually decreases until just before I get up in the morning. Also, my metabolism gradually slows until then. I am focused on that most critical point, just before dawn.

    According to Wikipedia "Metabolic Equivalent", 1 MET = 58.2 Watts per square meter. While sleeping, a human body emits 0.9 MET = 52.4 W/m2 so that's what I assume for my metabolism. Different people have different metabolisms so your results may be a little more or less than what I measured. I have noticed that I am warm enough to sleep well when my skin temperature is 93 degrees F, which is consistent with assumptions made by others. My interest in measurement is to have enough insulation to maintain this temperature.

    During the day I normally don't worry about being cold. If I have enough insulation to stay warm while sleeping, I'll have enough for the daytime. Before going to bed, my metabolism is twice or more what it is when I'm sleeping. I wear half of my sleeping insulation, a synthetic vest, before going to bed, so I am warm enough. If I'm cold I can exercise more vigorously or get into my sleeping bag.

    So, my investigation focuses on what it takes for me to stay warm using those assumptions - 52.4 W/m2 and 93 F.


    • Introduction
    • The Aim of this Article
    • The Basics
    • Calibration/Verification/Errors
    • Using Temperature Difference rather than clo
    • Repeatability
    • The Theoretical Conduction of Air
    • Boundary Layer
    • Verification Summary
    • Radiant Heat Loss
    • Radiant heat loss for different base insulations.
    • Radiant Heat Loss for Different Locations
    • Observations:
    • Theoretical Explanation
    • Summary:
    • Difference in Heat Loss for Several Different Materials
    • What Happens if Foil is Suspended Above
    • Radiant Heat Loss with an Air Space Under Foil
    • Convective Heat Loss
    • Summary

    # WORDS: 8400
    # PHOTOS: 31

    --- End of free preview ---
    Member Exclusive

    A Premium or Unlimited Membership* is required to view the rest of this article.


    * A Basic Membership is required to view Member Q&A events