What Makes Fabric Cool?

Defining Coolness in Fabrics

Seeing the word cool will automatically cause people to mistakenly think of these fabrics as portable air-conditioning units which can constantly make you feel cool. The reality, however, is that, when we are referring to these sorts of fabrics, we are not only talking about the direct sensation of coolness (contact cooling).

In fact, in an environment that isn’t highly humid, these fabrics can drain the sweat from the skin and allow clothes and skin to dry quickly. This ability to stay fresh also contributes to the cooling effect. Since your body temperature will not continue to rise, the heat will be exhausted, this causing your temperature to drop. When the body temperature and environment reach a thermal balance, the cooling effect ceases.

The Theory Behind Cool

When we feel cool, it’s actually our body temperature going down, but how can we lower our body temperature in the first place?

The main heat dissipation mechanisms within the human body are affected by environmental radiation, convection, conduction, and evaporation.

Thermal conductivity: Different materials have different thermal conductivity. Materials with good conductivity are more likely to impart a cooling sensation, whereas materials with poor conductivity will feel warmer.

Thermal convection: Thermal energy is transferred from a high temperature place to one with a lower temperature. For example, in winter, the room temperature is usually lower than the temperature of a given fabric. In the same way, when you first put on a feather jacket, your skin will feel cool at first, because your body temperature is higher relative to the material, causing the heat from your body to flow onto the material and therefore causing you to feel cool.

Cooling through evaporation: When we sweat, heat also dissipates, but if it is retained by the material of our clothes, it may cause us to feel damp and stuffy. When sweat is allowed to evaporate and dry quickly, it can also help us cool down.

It is important to mention that the easiest way to stay cool is to simply move away or block out the source of heat. For example, clothing allows us to stop solar radiation from directly hitting our skin. Studies show that the body temperature of someone wearing regular clothing in the sun is lower than that of someone who is naked. The well-known fabric manufacturer Schoeller uses this principle in its Coldblack line of yarn, which are applied to fabrics in order to keep the body temperature from rising.

All of the above means that, in fabric design, any factor that affects radiation, convection, conduction or evaporation may also affect the overall cooling properties of the fabric.