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Introduction

In the fall of 2022, I embarked on cold-weather camping with my newly purchased Zpacks Duplex, quickly discovering the tent’s susceptibility to heat loss and condensation issues. Despite various modifications and upgrades to my sleep system, including a higher R-value sleeping pad and a radiant barrier, I continued to experience significant cold and dampness. Through extensive field testing using temperature and humidity sensors and infrared imaging, I identified that the tent’s Dyneema fabric was highly transparent to infrared radiation, akin to standing in front of an open window, leading to substantial heat loss. This study delves into the intricate heat exchange mechanisms in tents, revealing that fabric transparency to infrared radiation plays a crucial role in thermal comfort, and proposes optimized tent setups for improved cold-weather camping.

Table of Contents

The Problem

I thought the biggest problem with the Duplex was the high fly pitch (discussed in our review) that allowed cold winds to blow through the tent. I made modifications to seal the vestibule doors and the horizontal ventilation screens at the tent ends (as best I could, but some wind still got through. I was still cold.

I purchased a Thermarest Xtherm sleeping pad (R-value 6.9) to replace an older Sea to Summit sleeping pad (R-3). I was still cold.

I was also getting wet from frozen condensation. I was getting condensation in the tent when I was not even in it!

I used temperature and humidity sensors to monitor what was happening inside and outside the tent.

My infrared imager revealed that the tent’s walls were getting colder than the outside air after the sun went down.

I experimented with fabricating and installing a radiant barrier that I attached to the tent canopy. The barrier met with some success but drastically increased the tent’s weight, and the barrier could fail in elevated winds.

I purchased a Durston X-Mid Pro to enjoy several features, including the ability to pitch the fly to the ground. The low pitch did improve tent comfort. I equipped the tent with a radiant barrier, improving its resistance to condensation in cold weather and raising the interior temperature by several degrees. I installed additional reflective panels over interior net areas. The latter additions did not produce measurable performance improvements. These modifications more than doubled the tent’s weight, increased its packed size, and were not sufficiently robust to survive high winds. I abandoned this approach and decided to study the heat exchange mechanisms at work in tents used in cold weather conditions.

Here is a photograph of the barrier in action:

tent with reflective material attached to canopy
Durston X-Mid Pro with a reflective radiant barrier attached to the upper canopy. I installed this to increase the interior temperature of the tent at night, to improve condensation resistance in cold weather.

Using my infrared imager, I determined that the Dyneema fabrics in my tents were transparent to infrared radiation, making them somewhat like standing in front of an open window. There were other issues to investigate:

  • Would switching to polyester or nylon tents reduce radiant heat loss?
  • Would different ventilation strategies minimize condensation?
  • Would double-wall tents increase warmth and mitigate condensation?

I purchased a small portable thermal imager to supplement my laboratory thermal imager in evaluating the behavior of tent fabrics and tent wall configurations.

I spent dozens of nights gathering data in various tents in various weather conditions.

Eventually, I began to understand the complex heat exchange mechanisms between the tent occupant and the outside environment. I also created new test procedures to measure tent construction’s impact on comfort.

In this article, I will describe what I learned and, using this knowledge, how to maximize tent comfort in cold weather while minimizing pack weight. In the near term, I will write two articles. This article will concentrate on thermal comfort, and the following article will discuss condensation.

My Findings: A Summary

  1. Your tent is a secondary system for keeping you warm in the winter. Your sleeping bag (or quilt) and a high R-value sleeping pad are the primary tools for keeping warm in cold weather. They must have enough warmth to insulate against the coldest temperatures you will encounter.
  2. Double-wall tents are not much warmer than single-wall tents, certainly not enough to justify the extra weight, bulk, and complexity. Changes in tent fabric will not increase the warmth of your tent, either.
  3. Your tent will balance heat transfer to and from the sky, the ground, the surrounding air, and you.
  4. Radiant heat transfer from the tent to the clear sky reduces the surface temperature of the tent walls to below the ambient temperature, causing the interior air temperature in the tent to drop below outside temperatures.
  5. When tent wall temperatures drop below the outside air temperature, heat transfers from the outside air, and, at times, the ground will halt the temperature drop inside the tent and cause it to remain close to the outside air temperature.
  6. Outside air temperature is the most significant determinant of interior tent temperature.
  7. The amount of heat produced by the tent occupant in a sleeping bag has minimal impact on the tent’s interior air temperature. The warmer the sleeping bag, the lower the occupant’s impact on the tent’s interior temperature.
  8. Ventilation is vital to influence humidity within the tent. As long as the quantity of ventilation does not result in breezes through the tent (which increase convective heat losses), ventilation has minimal impact on the tent’s interior temperature.
  9. A cold-weather tent that minimizes weight and provides the best thermal comfort will be a single-wall tent constructed from the lightest fabric consistent with expected snow and wind loading demands. I have chosen Dyneema for my cold-weather tent. Since this tent is for cold weather, screens, interior netting, or interior structures are unnecessary. The tent’s ventilation design should provide for protected, adjustable openings. Your tent’s design or pitch to the ground (or snow) must eliminate wind and spindrift in the tent.
  10. The tent shape, support, and pitching mechanisms must meet the expected environmental conditions. I avoid winter camping when severe weather is forecast. So far, a trekking pole tent is adequate for my needs.
  11. Pitching your tent beneath a cloudy sky or a dense tree canopy is the cheapest and lightest way to increase interior air temperature..

I conducted extensive testing and measurement to reach my findings and conclusions.

I used the following tents:

Tent #Model# wallsFabric
1Tarptent DiPole 1 2W2Polyester
2Tarptent Notch Li2Dyneema
3Durston X-Mid 1 Solid2Polyester
4Durston X-Mid 1 Fly Only1Polyester
5Durston X-Mid 22Polyester
6Zpacks Duplex1Dyneema
7Durston X-Mid Pro 21Dyneema
8Durston X-Mid Pro 2+1Dyneema

Weather conditions were generally clear to partly cloudy, with calm to moderate winds (up to 20 mph) and temperatures from the mid-30s to single digits (°F). Humidity ranged from 95% to 40%.

Unfortunately, I could not consider all tent constructions and weather conditions, so my findings and conclusions are likely incomplete. However, I hope the information I provide here will enable the selection of cold-weather tents that best meet user needs.

When I set out to write this article, I had a pretty straightforward set of expectations on how it would end. I was wrong!

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