How does woolen fabric keep the body warm?

Although preferences in clothing vary, everyone wears thick clothes during winter. During this time, woolen fabrics are in the highest demand. Have you ever wondered how these fabrics keep our bodies warm?

Throughout the day, we wear woolen clothes while moving about, and even at night, we rely on them. No, I’m not suggesting you sleep wearing a jacket! Rather, the blankets or quilts we use at night are usually made of wool. If you press these items, you’ll notice they compress easily. This happens because woolen fabrics trap a significant amount of air. You might wonder—what’s the connection between woolen fabric and air? There is a connection, but first, let’s understand how heat transfer works.

Heat moves from one place to another in three ways: conduction, convection, and radiation. For the first two methods, a material must be in contact with a source of higher temperature to increase its own temperature. In the case of radiation, no medium is required. Heat energy transfers in the form of electromagnetic waves, which is how heat travels from the sun to the Earth.

Our body generates its own heat using molecules and atoms derived from the food we consume. This internal process ensures our organs function properly, making us less dependent on external heat sources. However, heat has a generous nature—it flows from areas of higher temperature to lower temperature, much like water flows downhill. In other words, heat moves from warm objects to cooler ones.

When the rise of temperature in surroundings goes below that of our body, heat produced by our body starts flowing to the relatively cold surroundings until equilibrium is attained. That's where the roles of woolen fabrics are introduced. They act as a barrier that slows down the transfer of temperature between our body and the environment. The woolen fabrics themselves do not produce heat. Rather, the temperature of the body gets trapped inside, thus making us feel warm.

But how exactly do woolen fabrics act as insulators?

If you observe closely, you’ll notice that woolen fabric is not smooth like the threads of ordinary fabrics. Woolen threads are made of countless tiny, crimped fibers. As a result, the weave of woolen fabric is not as tight as that of regular fabric. These crimped fibers create tiny gaps, which trap air. And here’s where the magic happens.

On one side, the closely packed molecules of the solid wool fibers form a tight barrier, and on the other side, the entrapped air, having loosely packed molecules, acts like an insulating layer. Thus, they both together form a great ambiance that resists the transfer of heat either by conduction or convection. Therefore, woolen fabric acts as a very good insulator.

This explanation simplifies the concept for easy understanding. In reality, the process is much more complex.

The human body continuously produces heat. If all that heat were completely trapped, we’d basically overheat and "cook" ourselves in our own warmth. But that doesn’t happen because woolen fabric doesn’t block heat completely. A little heat is always leaked to the environment, and some is lost by the means of radiation.