The Effects of Kilt Yardage on Body Heat Loss

[Tartan Hiker]

Analysis
The graphed data for the three kilts can be seen in Figures 1, 2, and 3. In addition to the graphs, all data (temperature in degrees Centigrade; to the first decimal place beyond zero) were stored in tabular form. These data were used to derive the descriptive statistics located in Table 1. Note that the LabQuest collected four temperatures each minute, for a total of 61 data points in each 15 minutes test period.
Ambient temperatures. Throughout the test period, ambient temperature varied from a high of –1.8 degrees C to a low of –2.5 degrees C. Averaging all the ambient temperature data produced a mean of –2.01 degrees, and the median was exactly –2.00 degrees. Since this range was so narrow, I felt justified in using –2.0 degrees as the ambient temperature for all comparisons.
Statistical treatments. Student’s t-test of sample means was the method of choice for comparing the data derived in this study. Since the ambient temperature varied insignificantly, I was able to directly compare the temperatures (degrees Centigrade above ambient temperature, which in this case was recorded temperature plus 2 degrees), rather than calculate the differences between recorded and ambient and compare the remainders. Significance was established at p <0.05 level and high significance at p <0.01.

Examination of the derived data reveals a number of observations which are of considerable interest in this study. The following is a list of these observations, each accompanied by a brief discussion.

1. Rear standing temperature. When standing still, there was no significant difference in the average temperatures in the rear of the 4-yard and the poly/cotton kilts. The temperature in the rear of the 8-yard kilt was 5.25 degrees higher, an increase of 25% over the 4-yard and the poly/cotton.
When standing still, the air in the rear of the 8-yard kilt was 26 degrees C above ambient temperature. (That’s 79 degrees F warmer than the outside air!) Both thickness and composition affect the R value of fabrics, but the air trapped between the layers of fabric also play a significant role. With 31 deep pleats in the 8-yard test kilt, there is a considerable amount of material and dead air space, producing an exceptional insulative layer. As a result of this finding we reject the first hypothesis and accept the alternate hypothesis, that being that the 8-yard kilt is indeed warmer than either the 4-yard kilt or the poly/cotton kilt while standing still. I believe that the poly/cotton and the 4-yard compared favorably (surprisingly so) in large part due to the larger amount of trapped air in the knife pleats of the poly/cotton kilt (3” deep pleats with 1.5” reveals), as well as the multiple thicknesses of fabric (five in most places) which compensated for the poly/cotton fabric’s lower R value.

2. Front standing temperature. When standing still, the front of the poly/cotton kilt retained the least heat. The 4-yard wool kilt was warmer by 2.0 degrees, which was found to be a statistically significant difference. The 8-yard kilt was 2.4 degrees warmer than the poly/cotton. The difference between the front standing temperatures of the 4-yard and the 8-yard kilts was not statistically significant.
This finding leads us to accept the second hypothesis, that being that the 8-yard kilt and the 4-yard kilt exhibit no difference in warmth in the front while standing, but that they are both warmer than the poly/cotton kilt. The R value of the poly/cotton fabric is certainly less than that of 16-ounce wool, so in head-to-head competition, two layers of wool conserved more heat than two layers of poly/cotton. Since the construction of the aprons of the two wool kilts was essentially the same, there was no difference in their front standing temperatures.

3. Rear final walking temperature. After five minutes of walking, there was no significant difference between the rear air temperatures of all three kilts; the air temperature in all three kilts had dropped to approximately ten degrees above the ambient temperature. It is noteworthy that walking resulted in the 8-yard kilt losing 61% of its retained heat. With a 56% heat loss, the poly/cotton heat loss appeared to be less than that of the 8-yard kilt, and with a 51% heat loss the 4-yard box-pleat also lost less than the 8-yard kilt. Statistical analysis demonstrated no significant difference between the heat loss ratios of the 8-yard kilt versus the poly/cotton kilt, but did indicate that the 4-yard kilt lost significantly less heat when compared to the 8-yard.
Obviously air movement is a major factor affecting kilt “warmth.” My explanation for these data is that the extra swing generated by the mass of the 8-yard kilt’s pleated section, combined with the tendency of the pleats to open and close (“splay”) as they swing, contributed to the precipitous decline in rear temperature. Observations seem to indicate that while walking the pleats of both the box-pleated and the poly/cotton kilts do not splay as much as do the pleats in the heavier 8-yard kilt (although I have no quantifiable data to support this claim). If this is indeed the case, the air trapped between the layers of fabric would be exchanged more efficiently by the greater “bellows effect” in the 8-yard kilt, resulting in a more significant loss of heat. The more modest swing of the other kilts resulted in less air exchange, and therefore less heat loss.

4. Front final walking temperature. As was the case with rear temperatures, the front temperature of the 8-yard kilt dropped significantly more (40%) than did the front temperatures of the 4-yard and the poly/cotton kilts (11% and 15% respectively), although all these declines were less dramatic than the declines in rear temperatures.
I conclude that the bellows effect is at work here as well, and that the “flushing” of trapped air by the swinging pleats in the rear of each kilt also serves to flush warm air from the front of the kilt, albeit to a lesser extent. It is noteworthy that during the tests I was not wearing a sporran in its usual position. It is possible to speculate that heat loss from the front of a kilt may be reduced by wearing a sporran, which could serve to limit the movement of the front aprons and possibly reduce flushing of the air beneath them by the movement of the front aprons.