Building insulation materials is used depends on a wide variety of factors. Some insulation materials have health risks, some so significant the materials are no longer allowed to be used but remain in use in some older buildings such as asbestos fibers and urea. Factors affecting the type and amount of insulation to use in a building include: Considerations regarding building and climate: Often a combination of materials is used to achieve an optimum solution and there are products which combine different types of insulation into a single form. Spray foam is a type of insulation that is sprayed in place through a
Cavity wall insulation cavities, a fibrous material such as cellulose insulation or glass wool is blown into the cavity through suitably drilled holes until it fills the entire wall space. Foam can also be used for this purpose. Although some foams used in the past, such as urea-formaldehyde, are no longer used (some people are allergic to this material, which is very difficult to remove once inside the wall), others, such as polyurethane, have taken their place. Cavity wall insulation also helps to prevent convection and can keep a house warm by making sure that less heat is lost through walls; this can