Saving body heat.

The-most important heat to save is your body heat. If your body gets too cold' it won't work properly. Then you are said to be suffering from hypothermia.

You are unlikely to suffer from hypothermia - as long as you have shelter, enough clothes to wear (and, of course, "enough to eat). But some people like divers, mountaineers and astronauts, live and work in more extreme conditions. For them, hypothermia is a real problem. They have to wear special clothes to survive.

For divers, the problem is caused by the cold sea water. The moving water quickly carries heat away from the skin.

Those divers who work in shallow waters wear wet suits to stay warm. These suits are made of rubber which has bubbles of air trapped in it. Surprisingly, the suits also use water as an insulator. A thin layer of water is trapped between the suit and the diver's skin. Being a poor

conductor, this water helps to prevent the diver's body heat from escaping.

Mountaineers face dangers from sub-zero temperatures, and from driving rain and snow. If their clothes become soaked through, they quickly become chilled. They normally wear waterproof outer, and heavily insulated inner clothing to help them survive. Until recently, however, this arrangement of clothing did not allow water vapor {from sweat) to escape, and so the mountaineers, clothes became wet with condensation.

Modern fibers solve this problem. The most up-to-date waterproof clothing allows water vapor to escape. The newest insulating fibers soak up very little water.

Astronauts face all sorts of dangers. A 'space suit' contains several layers, each of which protects the astronaut from a particular danger. There are layers for protection against fire, cosmic rays, and flying particles. There are also several insulating layers which protect the astronaut against the extreme temperature which he meets outside the spacecraft. In fact, the astronaut is so well insulated that his body heat can't escape' He needs a cooling system to prevent overheating! He carries a small refrigerator on his back. Cold water from this refrigerator flows through small pipes in the astronaut's underwear and takes away some of his body heat.