Protective clothing for the body comes in several styles and is designed for a number of specific purposes. There is a trend toward lightweight, yet durable, clothing and one material that possesses these characteristics is nylon scrim coated with polyvinyl chloride, often used to create clothing which is resistant to water and moisture penetration. This waterproof material has self-extinguishing properties that make it fire retardant, and it resists the attack of most chemicals as well as mold, fungus and mildew. Because concrete construction now proceeds in almost all kinds of weather, protection from extreme temperatures is a common clothing requirement. Insulated hoods, jackets, and trousers with wind-tight nylon linings are in demand more than ever before. This kind of clothing traps air, and keeps the body form losing too much of its heat production. Concrete workers who must work over or near water should be equipped with industrial life jackets. Vests made of expanded plastic foam won't waterlog, mat, mildew or rot, and they're not affected by gas, oil, acid or salt water. The jackets are designed to turn the wearer face up in the water, even if he is stunned or unconscious. No part of the human anatomy needs greater protection than the head. Contractors and builders should require that all employees wear safety hats at all times on construction jobs. Besides its hard exterior surface, the safety hat should have a flexible inner cradle. A fixed upper cradle will provide built-in protection, while a lower cradle can be adjusted to the wearer's comfort.