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Wicking - Why is Wool warm and Cotton cool?

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Why is cotton cool?

Cotton can also absorb water, and thus can store both latent and sensible heat the same as wool. The difference is that wool still acts as both insulator and thermal capacitor when it is wet, whereas the cotton is more likely to be saturated, which effectively short circuits heat directly away from the body, and so the body loses heat as though it were naked and soaking wet, even colder because they can effectively increase the surface area for evaporation while providing a negligible amount of insulation.

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Cotton is cellulose and it is microscopically present as thin walled hollow tubes. Water will evidently "plasticize" the cellulose and allow the collapse of the thin walled hollow tubes. This geometry change would exhibit a strong effect on the thermal conductivity.

It is said that this accounts for the visual aspects of the "Wet Tshirt" effect which elicits whistles and shouts.

A thoroughly wet Tshirt would allow a continuous path of water to act as a high conductivity path acting in parallel with whatever insulation capabilities collapsed thin walled cellulose tubes exhibit. In effect, this could act as a thermal conduction "short circuit".

Really wet wool would also exhibit the same "short circuit", but people commonly claim that if wool gets drenched, wringing it out and putting it back on the body quickly results in a drier and warmer situation. This could also work the same way for synthetic fabrics.