An Introduction to Synthetic Insulation Degradation

Synthetic insulation degradation (e.g., loft and thermal performance) has been a long-time concern in the backpacking community. In July, I wrote an article that explored this topic and described how well two types of synthetic insulation, Climashield Apex 6 osy (ounces per square yard) and Primaloft Gold 6 osy withstood ten cycles of washing and drying. In that article, Climashield Apex demonstrated almost no loss of thermal performance. Primaloft demonstrated minimal loss of thermal performance at about 9%.

Both types of insulations can withstand repeated washing and drying with little loss of performance.

However, backpackers subject their sleeping bags and garments to another form of torture that results in synthetic insulation degradation: compression. Compression occurs when packing garments or sleeping bags into stuff sacks. This can occur repeatedly during a multi-day activity.

In order to quantify the impact of compression cycles and weight on synthetic insulation degradation, I wrote this article. In the article I concluded the following:

  1. Minor thermal degradation appeared to result from multiple compressions.
  2. Degradation is not influenced by the magnitude of compression, within the compression range studied (0.22-0.88 pounds per square inch).
  3. The number of test cycles included in the test was insufficient to make final conclusions as to whether significant deterioration would result from compression and that further testing was required.

In this follow-up article, I present the results of 21 additional compression cycles on synthetic insulation degradation. In summary, what I found is as follows:

  1. Loss of thermal performance due to compression of both Climashield Apex and Primaloft Gold are minor. Primaloft performs slightly better than Apex. Degradation of Apex is about 2% per compression. Degradation for Primaloft Gold is about 1%.
  2. Loss of loft in both insulations is negligible. The loss of loft per compression cycle is about 0.2% for both Apex and Primaloft.

There will be a Part III article in which I place the insulation in a protective sleeve, and randomly (but lightly) stuff it into a stuff sack and then repeatedly compress and measure thermal performance. The purpose of this study will be to increase tortuous stress on fibers to see what impact that has on synthetic insulation degradation. Those results will be available in a month or two.

How We Tested Synthetic Insulation Degradation

Note: The test methodology described below is reproduced from the Part 1 article. I have noted changes for Part 2 in bold.

Compression in the field takes place through two very different mechanisms:

  1. Stuffing, in which a garment or sleeping bag is loaded, under some pressure, into a stuff sack.
  2. Utilization pressure. This pressure may result from lying in your sleeping bag or the weight of a backpack on jacket insulation. Part of this pressure may occur beneath backpack straps or may occur due to the pressure of the pack itself on the underlying insulation.

I chose to attempt to replicate pressure placed directly on insulation in the bottom of a sleeping bag by an average male as a model for encouraging synthetic insulation degradation. I estimated pressures exerted by the average adult male using references 1 and 2. Based on these sources, I assumed an average body weight of 202 pounds and an average skin surface of about 25 square feet.

The average pressure exerted on the bottom of a sleeping bag was calculated to be approximately 0.14 pounds per square inch.

Two types of insulation were tested: 6 osy Primaloft Gold and 6 osy Climashield Apex. Four samples of each were cut from unused insulation to fit my guarded hot plate. Each sample was compressed by placing concrete pavers on each sample. Each paver weighs 23.4 pounds. Sample 1 received 2 pavers, laid side by side, which produces approximately the same pressure as our average male. Sample 2 receives 4 pavers. Sample 3 receives 6 pavers. Sample 4 receives 8 pavers. Thus, sample 4 receives about 4 times the pressure produced by our average male. In Part 2, samples 2 and 4 are eliminated. Only samples 1 and 3 are tested.

Samples were compressed for approximately 24 hours. After 24 hours, samples were removed and allowed to recover for about 10 hours. In Part 2, samples are compressed for 12 hours and allowed to recover for 12 hours. Next, the samples were tested for thermal resistance (R-value) on the guarded hot plate. In Part 2, 3 compression/recovery cycles were repeated. Then, the samples were removed and tested for thermal resistance. Each test ran for 1 hour. Any test result that appeared to show elevated deviation was retested. Prior to testing, each sample sat on the hot plate for 20 minutes. The guarded hot plate surface was maintained at 100 °F +/- 0.2 °F (38 °C). The ambient 20 inches (51 cm) above the guarded hot plate was maintained at 71.5 °F +/- 0.5 °F (22 °C)

Each sample was measured for loft following the recovery period. When fabric thickness is measured, a weighted plate is placed on the test sample and the distance from the underside of the plate to the sample mounting surface is measured. High loft insulation cannot support much insulation without compressing, so the weight of the plate must be selected carefully. In this case, a rectangle of extruded polystyrene foam with additional small lead weights was used. This plate, along with weights, weighs 5.1 ounces (145 g). A Mitutoyo Digimatic caliper was used to measure the distance from the underside of the plate to the mounting surface. Two measures were taken near corners on each long side. The resulting four measurements were averaged to calculate the loft to the nearest hundredth of an inch. By necessity, this is a somewhat compressed loft. The actual non-compressed loft is unknown and not easily determined due to thickness variation across each insulation sample. Since the sample sits on the guarded hot plate without the 5.1 ounces (145 g) imposed by the measurement plate, the sample loft on the guarded hot plate will tend to be greater than the measured loft. Our loft measurement provides a physical loft dimension that reflects changes in the fabric resilience which will track changes in the compressive strength of the sample fibers. Thus, thermal performance measurements on the hot plate cannot be expected to track measured loft except in the case of substantial changes in measured loft. Substantial changes in loft did not occur.

Figure 1 shows the compression set-up.

The author's garage with testing gear set up to test synthetic insulation degradation. From the bottom up: Cork pad, Rip-stop fabric, Insulation Sample, Rip-stop fabric, cork sheet, concrete pavers. As can be seen, for each sample, insulation is completely crushed under the weight of the pavers.
Figure 1: Test Setup. From the bottom up: Cork pad, Rip-stop fabric, Insulation Sample, Rip-stop fabric, cork sheet, concrete pavers. As can be seen, for each sample, insulation is completely crushed under the weight of the pavers.

Test Results

  • Table 1 shows physical data for the two sets of four insulation samples.
  • Table 2 shows “as found” R-value and R-values measured after each of the 9 compression tests.
  • Table 3 shows “as found” loft and loft measured after each of the 9 compression tests.
  • Table 4 shows “as found” loft and loft measured after compression tests 10-30.
  • Figures 2 and 3 show graphical results of the R-value data and Loft data for Climashield Apex, Compressions 1-9.
  • Figures 4 and 5 show graphical results of the R-value data and Loft data for Primaloft Gold, Compressions 1-9.
  • Figures 6 and 7 show graphical results of the R-value data and Loft data for Climashield Apex, Compressions 1-30.
  • Figures 8 and 9 show graphical results of the R-value data and Loft data for Primaloft Gold, Compressions 1-30.

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