Comparative test of the thermal insulation of down jackets

  Two down jackets were tested: one from the K-Way brand and one from the Penfield brand (sleeveless) Two types of tests were carried out:

• using a heating film placed inside the down jackets;
• by measuring the losses through the down jackets when they are worn by a person.

In both cases, the objective is to determine a characteristic which accounts for the quality of the insulation of the garment. We have chosen to determine the thermal resistance (which will be noted R below) by analogy with the insulation of buildings. The higher the thermal resistance, the better the insulation. The area studied each time is the center of the back of the down jacket. The thermal resistance is the coefficient of proportionality between the heat flow and the temperature difference: where is the temperature difference between the two sides of the insulation, R the thermal resistance and the thermal flow. For a compact material, the thermal resistance is calculated as follows: Where is the thickness of the insulator and is the thermal conductivity of this insulator. 1 °) Tests with a heating film (indoors): To carry out these tests, the down jackets were placed open on a table on a plate of insulating material placed on a table. A heating film is placed between the insulation and the down jacket (in the center of the back of the garment. The temperature is measured under the garment with a thermocouple and outside with a thermal camera. To determine the amount of heat lost through the garment, we use a device called “Fluxmeter”. The heat flux here represents the amount of heat (Joules or Calories) passing through the garment in one second. Figure 1 shows the support and the heating films. Figure 2 shows a view of ‘a fluxmeter and a thermocouple fixed inside a down jacket Figure 3 presents a view of the down jackets positioned on the table Figure 1: View of the support and the heating films Figure 2: View of a fluxmeter and a thermocouple attached inside a down jacket (K-Way)

Figure 3: View of down jackets positioned on the table during an indoor test (K-Way on the right )

Figure 4: Thermal images of the outside of the down jackets during tests with a heating film (inside); K-Way on the right Figure 4 presents the thermal images of the outer surface of the two puffer jackets. These are images in false colors which allow you to visualize the distribution of the losses: the rather blue or black areas are the areas where the losses are the least significant. The clear areas (yellow or white) are those where the losses are the most important. We notice that the seams appear lighter, a sign that the losses in these areas are greater. Two tests were carried out. The measured values ​​of temperature and flow are presented in table 1. From these measurements, one can calculate the thermal resistance of the down jacket: it is the value of the difference of temperature inside-outside divided by the flow which crosses clothing. The indoor air temperature was 21 ° C and the relative humidity 50%. Note that the K-Way down jacket has a thermal resistance about 3 times lower than the other down jacket. This means that for the same temperature difference, it lets around 3 times more heat through. Table 1: Results of the indoor measurements 2 °) Tests on people (outdoors): In this second case the down jackets were worn by two people. Two measurements were made. Between these two measurements, the two people exchanged the down jackets. The sensors were positioned in the same place as for the other tests. The two people put on and closed their down jackets inside, then went out. The measurements were made a few minutes after their release. The only difference from the first type of test is that it is the people who heat the inside of the down jacket. The outside air temperature was 13.5 ° C and the relative humidity 68%. In Figure 5, we see the two people during the second measurement. Figure 6 shows the corresponding thermal images (back and front). Table 2 shows the measurement results.

Figure 5: Photographs taken outdoor

Figure 6: Thermal Images taken outside (back and front)

Table 2: Outdoor Measurement results There are higher thermal resistance values ​​than the first method, probably due to poorer contact between the back and the flowmeter attached to the jacket, therefore an additional layer of insulating air. However, this phenomenon is observed for the two down jackets. The thermal resistance of the K-Way model is approximately 3 times lower than that of the other model, which confirms the previous results.