Thermal engineering of skirts

[pelmut]

Is the thermal conduction through a single-layer skirt increased or decreased when extra material throws it into folds? I've mused over this conundrum for some while and there appear to be two contradictory possibilities (described below). I wonder if some of the other engineers in this group can contribute some thoughts .

Conductivity 1.jpg

A) The conductivity is inceased because there is a greater surface area in contact with the air on both sides allowing more heat flow.

Conductivity 2.jpg

B) The conductivity is decreased because the air trapped in the folds acts as an insulator. If the folds are sufficiently convoluted, the effecive thckness of the skirt is increased and heat energy would have to travel longitudinally through the fabric to excape.

Conductivity 3.jpg

Are both A) and B) true, depending on the circumstances? What determines the point at which transition from greater to lesser heat flow occurs? Long 'full' skirts feel cool when you are moving, but warm when you stop; I always assumed that this was entirely due to air interchange when moving, but I wonder if the two conditions above also play a part? (If someone is looking for a subject for a PhD thesis, they could follow this up)

[crfriend]

Both A and B can be true, but motion, amount of trapped air under the skirt, and ambient conditions would have to be taken into account.

Motion (or wind) could push the lightly folded fabric in A into something more closely resembling B or flatten it out completely yielding something closer to the first image. "A" would be technically slightly warmer than a flat piece of fabric as it'll trap more air inside; the extra surface area likely would not come into play save for motion effects.

"B", on the other hand, is heavily folded enough to operate as a functional insulator on its own by trapping a second layer of air inside the folds, which will work with the naturally-occurring air trapped inside the skirt. Various heavy fabrics can mimic this by trapping air in the construction of the fabric itself.

From my experience with very long skirts, there is comparatively little direct air-exchange via the hem and this is further restricted with underskirts, especially those with ruffles at the hem (petticoats). In atmospheric settings with the level of heat that a body can generate we're dealing almost completely with conduction; that is the skin being in contact with air (inside the skirt) with a barrier (the skirt itself) between the "inside" air layer and the external atmosphere. Radiation may play a small role, but it's likely negligible. Convection, the 3rd main transfer mechanism, will keep the upper portion of the skirt warmest and the lower confines cooler; motion, however, will overcome that effect trivially.

So, there's the theory as I understand it, and it explains why a skirt can be warmer than trousers during the winter and cooler than trousers in the summer -- a firm win in both cases. The effect can be enhanced or reduced by fabric selection and how full the skirt is, with fuller skirts generally trapping more air inside them. in either case, lighter fabrics will allow more direct airflow through the fabric and contribute to "dumping heat" which is useful in summer.

[Caultron]

Just put one on and test -- day after day after day...

Have to find a control group, though, and where's the fun in that?

[skirted_in_SF]

Obviously B would work as an insulator, it looks just like the symbol architects use for an insulated wall.

[Taj]

May be looking at the difference between men and women here. A man would analyze such a thing. A woman would ask another woman (mother perhaps) which skirt would be warmer. They would solve it accurately through experience.

[skirtyscot]

No, a woman would put her jeans on, with tights underneath if it was cold outside!

[Taj]

True, too.