Using clothes to keep warm
There are millions of tiny tubes just under your skin. They carry blood. The blood itself carries heat that has been made in different parts of the body. Normally, some blood runs through the tubes. Heat escapes from the blood into the skin by conduction. It then escapes from the skin into the air by conduction and radiation. This escape of heat from the body makes your skin feel warm.

When you feel cold, your skin does its best to help. It closes down the tiny tubes so that the blood cannot flow through them. The blood normally gives some colour to your skin but when it is kept away from it your skin becomes paler. By closing down the blood supply to the skin, the body saves heat to keep warm.

Under the skin is a layer of fat. This is a heat insulator. Heat from tubes of blood deeper in your flesh cannot pass through the fat so the fat also helps to keep you warm. As the body goes through procedures to save heat, your skin tries one last way to help. It raises the hairs on its surface to trap air and make a layer of insulation. As we only have a thin covering of hair compared to other animals, this attempt does not work. It means that now we have to help our body save heat.

We do this by putting on clothes. You may think that any kind of material would do to make clothes but you would be wrong. The skin has a heat-releasing process, which must be considered. When the body is too hot, the skin releases sweat. Even when the body is warm a small amount of sweat is released. The clothes have to be able to deal with the sweat because the sweat changes into a vapour in the air. If this sweaty vapour is trapped in the clothes it makes them damp and uncomfortable. This means that clothes must keep us warm but also let sweaty vapour escape from around the skin. They must do two things to make us comfortable - they must keep us warm in cool conditions and, having made us warm, they must let us remain comfortable by letting sweat leave our skins.

What makes clothes warm you up?
Clothes make a layer of insulation over the skin. This prevents heat from the skin passing into the cold air around the body. It is important to remember that heat passes from a warm place, such as your body, to a cold place, such as the air on a winter's morning. Coldness does not pass from the air to the body.

Can any kind of insulation material be used to make clothes?
No. The material must be light in weight. If it was heavy, it would be very tiring to wear. The clothing materials must also be flexible so they can change shape easily as the body moves. Wood is a lightweight insulating material but is not flexible so you would not make pullovers or trousers from it. However, hats, shoes and leggings have been made from bark in the past.

How do warm clothes stop heat moving through them?
They are made from a material which can hold a layer of air. The material is made of fibres and the air is held between them. The layer of air prevents heat moving by conduction through the material.

How does sweat pass through clothes?
There are tiny gaps between the fibres which are too small for large amounts of air to pass through. When there is a large amount of vapour or gas in one place and a small amount in another place the vapour or gas moves slowly to the place where there is a small amount. This way of moving is called diffusion. There is a large amount of sweat vapour in the air next to the skin and hardly any on the outside of the clothing. This difference in the amount of vapour lets the sweat move slowly through the gaps between the fibres to the outside of the clothes.

If sweat can move out of clothes can rain pass in just as easily?
No. The vapour can pass through the tiny gaps but the gaps are too small to let drops of rainwater pass through. The raindrops have to stay on the surface. Clothes, which have gaps large enough to let in rainwater, will eventually get soaked. Some clothing has a layer of insulating fibres with wide gaps covered by a layer of cloth with very small gaps. The layer of fibres with wide gaps provides the insulation and the layer of cloth with tiny gaps keeps out the rain. Clothes like these keep you warm and dry.

What were the first clothes worn by people?
The first clothes were probably capes made of leaves and plant stems. They were used to keep people dry rather than warm. As people moved into places with cooler weather, they made capes out of animals' skins to keep warm. These capes served both as clothes and bedcovers. In countries with cool weather, such as Denmark, people in the Bronze Age made felt and used it for clothing. Felt is made by pressing hot, wet, animal hair together. The Egyptians lived in a warmer country and made clothes from long fibres in the stems of flax plants. They wove these fibres together to make a cloth called linen. They used it to make their clothes. Linen was the first woven material which was used to make clothes.