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Why is cotton so cooling?
Question Date: 2020-06-23
Answer 1:

Cotton (presumably in the context of clothing) is cooler than many other fabrics because it is more breathable than most.

Breathability means that moisture vapor (basically humid air) flows easily through cotton relatively more easily than, for example, polyester. This air flow prevents hot air from being trapped near the wearer's body. The breathability comes from the shape of cotton fibers. As shown in the microscope photographs here, cotton fibers resemble twisted ribbons, which prevents them from stacking tightly together when woven. As a result, there are plenty of open spaces for air to pass through. In contrast, synthetic fibers are usually very smooth and straight "rods" (see photographs farther down the same page).

In addition, cotton is hydrophilic (water sticks to the fibers). This helps by wicking liquid water (e.g., sweat, moisture from air) away from the wearer's skin. In combination with airflow, this aids in evaporation of that water, providing an evaporative cooling effect which can be greater than that of damp bare skin. Evaporation helps to cool because the transition from liquid to vapor requires energy, which is taken in from the surroundings, thereby lowering the temperature of the surroundings. [Note though that cotton does not provide the most evaporative cooling - the structure of synthetic and shape of synthetic fibers means that some of them can transport liquid water more easily than can cotton, and therefore these can exhibit greater evaporative cooling than cotton. However, the structure of these fabrics also reduces their breathability, so they may still feel warmer than cotton.]

Answer 2:

Wearing cotton clothes feels cooling because cotton is "breathable." This means that air and water vapor can easily pass through the fabric. Usually, cotton fabric is not very tightly woven, so it has gaps for air and vapor to pass through. For comparison, think about wearing a plastic raincoat. Warm air (heated by body heat) can't pass through the coat and will stay in place, causing you to feel warm.

To estimate the breathability of a material, try holding it up near a light. If the material has larger gaps between threads, you will see more light through it, and chances are, it will be more breathable and feel cooler to wear.

Answer 3:

Hello Adrienne, you ask a very good and practical question. While I am no expert in textiles, I believe that the cooling powers of cotton come from the fact that cotton is not very dense and as a result, it has a lot of little openings that allow for air to travel through it.

As a result, sheets made from cotton can be cooling because the warm air that is trapped under the sheets can travel out and keep you cool underneath. On the other hand, you can think about a denser fabric like wool that is very much able to trap heat, making it much less cooling. Wool would make good sheets in the winter because it can keep you warm (traps the warm air under the blanket) but would be pretty unbearable in the summer. One more thing to consider is the thread count of the sheets/clothing you're thinking about. The higher thread count, the denser the weaving of the threads, and the greater the ability to trap heat.

Answer 4:

According to this site, cotton is soft, lightweight, breathable, and soaks up sweat, allowing heat to escape the body and for you to stay cool. ... If you are sweating a lot, cotton tends to soak up moisture so it could become heavy and wet, it may also show moisture stains by your armpits or collar if you wear it in light colors. Aug 21, 2019

Answer 5:

It's not.

Cotton clothes are less insulating than wool, because of the nature of the fibers, but cotton isn't itself any cooler than wool, nylon, or anything else.

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