Like this? Follow me:
Winter in Colorado! The outside temps dipped down again, so I planned on camping out to test my gear and see just how warm it keeps me in frigid conditions.
There are a few different parts of a holistic camping system that assist in providing a habitable environment. A shelter (tent), a sleeping bag or quilt, and the clothes you’re wearing. All these work to keep you dry and warm. In my survey, I was curious to see how each part contributes in adding warmth.
The setup was simple: during the night, I kept a thermometer right outside the tent, another hanging inside my tent, one fixed to the outside of my clothing, and a final one located right next to my chest. With all these thermometers, we should be able to see how much each part of the system contributes to my overall warmth when compared to the outside temperature.
Here are the results:
Outside Temperature
The outside temperature held steady at 0F/-17.8C (blue line) for the entirety of the night, making the rest of the results easy to interpret, with math simple enough even for me. How much warmth did the tent itself capture?
Tent Interior Temperature
After stabilizing, the temperature of the interior of the tent was around 12F/-11C (red line), about 12F/6.8C warmer than the exterior. Tents like the one I used — a Nemo Osmo 1P Tent — itself aren’t what I would call especially insulated, but there was a constant source of heat in the tent: my breath as well as whatever heat was lost from my clothes and sleeping bag. This rising warm air was then trapped near the top of my tent by the impermeable tent fly fabric where my thermometer was hung.
The two peaks in the chart correspond to when I went outside to answer the call of nature, which I can probably attribute to unzipping my sleeping bag and allowing the warm air that was trapped inside to be freed. I made those trips pretty brief (brrr!) and given the location of the thermometer in the tent, probably explains why there isn’t a dip afterwards.
How much heat did my sleeping bag hold onto?
Sleep Bag Temperature
The temperature between my clothes and sleeping bag showed the greatest variance in temperature (yellow line), with a high of 95.4F/35.2, a low of 52.7F/11.5C, and an average of 73.9F/23.3C. An ambient temperature of 73.9F sounds quite comfortable, and the 0F/-17.8C limit rating of my sleeping bag — a Sierra Designs Nitro 800 — that I was nestled within certainly proved reasonable.
On average, the inside temp of the sleeping bag was 61.9F/34.3C warmer than inside the tent. Quite a temperature difference! Looking at the graph in the whole and not to bury and lede, the sleeping bag provided the most substantial difference in temperature between anything we’re comparing. If there is one part of this system that is the most effective in trapping body heat to keep one warm, it’s the sleeping bag.
The variance in temperature is simple to explain. As well as getting up in the middle of the night a couple of times, I moved around which created more heat. Adjusting my position in the sleeping bag may also released additional warm air into the tent. This is more of a feature than a bug: the long zipper on the side of the sleeping bag, as well as the cinches on the hood help regulate the temperature. Unfortunately, I don’t have any video of me sleeping, but my guess is that constant temperature being recorded also corresponds to me enjoying a deep sleep.
Finally, what temperature was recorded between my clothes and myself?
Next to Skin Temperature
Next to skin temps were a smoldering 95.6F/35.3C (green line)! My clothing system consisted of a 250 g/sm wool base layer/underwear pair, as well as a generous 800 fill goose down jacket and pants. This is some serious supplementation to the sleeping bag, so it isn’t any surprise that I was almost uncomfortably warm all said and done. But the 95.6F/35.3C temperature was only 21.7F/12C warmer than what I logged between the sleeping bag itself and my clothing, meaning my clothes made less of an impact than the sleeping bag.
Conclusions
| Averages | Temperature (F) | Temperature (F) Difference: |
|---|---|---|
| Outside Temp | -0.01 | 0 |
| Inside Temp | 12.76 | 12.77 |
| Temp Sleeping Bag | 73.92 | 61.16 |
| Temp Next to Skin | 95.59 | 21.67 |
This was a fun survey to do, as it illuminated just how each part of a camping setup helps keep the sleeper comfortably warm at night.
Maybe the most surprising to me is seeing how much the tent holds onto ambient heat. I would be influenced to think one could pick a reasonable sleeping bag based on the ambient temperature of the tent, rather than outside temperature.
For this night out at 0F/-18C, and an interior temperature of 12F/-11C, a 10F/-12C comfort rated sleeping bag would be rational, all else being optimal. This ambient temp would also be different depending on the tent you’re using. I used a fairly small, one person tent, which I would think would hold onto more warm air than a larger, two person tent. Things get a little complicated when we consider condensation of the tent, which I will happily ignore in this small survey as being outside its pale, but condensation was present (if that matters) mostly above my head. Although not being reported for the sake of clarity, humidity was reported by the thermometers as being fairly constant.
Given the fairly constant, high temperature being reported next to skin, my layers both worked and were probably too much for the outside temperature I was camping in. I can self-report as never feeling cold. If anything, I felt a little too warm, but my body seemed to have been able to self-regulate. If it hadn’t been able to, my guess is that I would be shivering in an attempt to warm up, or would be forced to adjust my layers by removing them — or at the very least venting the sleeping bag. If I was to camp in similar conditions, I would go without the down suit, as it seemed to be unneeded on this night.
I would consider myself a warm sleeper, but I don’t know if there is any basis to that feeling, except that those who dare cuddle with me during the night sometimes have to remove themselves from the clutches of my loving arms as they themselves become uncomfortably too warm. I took these experiences as somewhat proof that my temperature in the middle of the night spiked, but I see no real data in this survey to support this. In the future, it would be interesting to monitor my temperature in a similar way while just sleeping inside in my regular bed.
There is somewhat of an old notion that one should sleep in a sleeping bag naked (or close to it), but unfortunately, I don’t feel this little survey I’ve done supports or rejects this idea very strongly. In my own mental model, I really see the sleeping bag and any layers you’re wearing as part of the same layering system, with the sleeping bag just being the outer layer. Differentiating them as separate entities isn’t necessarily helpful. Taken holistically, it’s no surprise that the temperature would be higher under the layers than when the temperature is measured between one layer and another.
Raw Data
Find the public Google Sheet here.
Thanks for reading.
