Tom Greenleaf, age 12, of Yarmouth, Me., for his question:

IS NATURAL OR SYNTHETIC RUBBER MORE WIDELY USED?

Rubber is an important product because it holds air, keeps out moisture and does not conduct electricity. Its chief importance to us is that it is elastic. We depend so much on rubber that it now would be almost impossible for us to get along without it. Manufacturers today make between 40,000 and 50,000 different products out of rubber. A typical car today uses about 550 rubber parts.

Rubber is one of man's most important raw materials. Natural rubber comes from the juice of a tree. Synthetic rubber is made from chemicals.

In making natural rubber, workers obtain a milky fluid from the bark of rubber trees which is called latex. They produce crude rubber by removing water and other substances from the latex. Machines then shape the rubber into sheets and other forms.

Synthetic rubber, on the other hand, is made by mixing chemicals to produce latex that looks like natural latex from rubber trees.

Tire production today ranks as the chief use for most of the world's rubber. Most tires contain both natural and synthetic rubber. The largest tires consist of more natural than synthetic rubber while automobile tires contain more synthetic rubber.

When the Japanese captured the leading rubber growing lands of Southeastern Asia during World War II, scientists of the Allies found ways to make synthetic rubber. And today, the world uses more synthetic rubber than natural rubber.

More than three fourths of the rubber used in the United States today is synthetic. Other important producers of synthetic rubber include Russia, Japan, France and Great Britain.

The leading rubber manufacturers of the world usually grow part of their natural rubber on their own plantations, and they produce synthetic rubber in their own plants. Many of the big rubber companies also produce plastic products because synthetic rubbers and plastics are much alike chemically.

Manufacturers obtain bales of dry rubber from plantations and from synthetic rubber manufacturing plants. Latex comes to them in big tanks on ships and in tank cars.

In the polyurethane family, there is no real dividing line between polyurethane rubbers and poluurethane plastics.

Manufacturers group synthetic rubbers into two types: general purpose and special purpose. General purpose rubbers can be used in place of natural rubber while special purpose rubbers improve upon nature.

Special purpose rubbers have special properties such as great resistance to grease, air and extreme temperatures that make them better than natural rubber for certain uses.