Barrier materials are substances designed to prevent the passage of gases, liquids, or other materials. They are commonly used in packaging, construction, and various industrial applications to protect products from environmental factors like moisture, oxygen, and contaminants. Examples include plastic films, metal foils, and ceramic coatings. These materials can be classified based on their properties, such as permeability and durability. For instance, polyethylene is often used for food packaging due to its moisture resistance, while glass is favored for its impermeability and strength. The choice of barrier material depends on the specific requirements of the application.