Kinetic Theory of Breathability

Kinetic Theory explains that heating a liquid causes an increase in movement energy of its molecules. With this increase in movement some molecules are able to overcome the attractive forces of one molecule to another and escape from the liquids surface.

This evaporation can be increased in several ways.

• Increasing the temperature and thus the kinetic energy of the molecules.

• Increasing the surface area of the liquid increases the opportunity for molecules to escape.

• Causing a draught to remove escaped molecules before they have a chance to return to the liquid (wind chill).

• Reducing the air pressure above a liquid, as this reduces the chance of an escaping molecule from bouncing off an air molecule and rebounding back into the liquid.

• Reducing the humidity of the air above the liquid, as this again reduces the chance of rebounding collisions..

Fabrics can also rebound molecules. The more breathable they are, the fewer they will rebound. A fabric’s tendency to allow molecules through without rebounding them is its breathability.

A cold fabric will tend to sap the energy of the molecule, perhaps capturing and condensing it, or allowing it to continue in a depleted state.

A hydrophobic (water repellant) fabric will tend to rebound a molecule.

A hydrophilic (water loving) fabric will tend to sap the kinetic energy from the molecule, often absorbing it as part of its structure and in the process releasing some energy in the form of heat – the Heat of Absorbtion.