Vermiculite and perlite insulation materials are commonly found as attic insulation in homes built before 1950. Vermiculite insulation materials aren't widely used anymore because they sometimes contain asbestos. However, according to the U.S. Environmental Protection Agency, asbestos is not intrinsic to vermiculite. Only a few sources of vermiculite have been found to contain more than tiny trace amounts. Still, if you have vermiculite insulation in your attic, do not disturb it. If you want to add insulation to your attic, use an insulation contractor who is trained and certified in handling asbestos.
Vermiculite and perlite consist of very small, lightweight pellets, which are made by heating rock pellets until they pop. This creates a type of loose-fill insulation with a thermal resistance of up to R-2.4 per inch. These pellets can be poured into place, used to fill concrete block cores, or mixed with cement to create a lightweight, less heat-conductive concrete.
Article source: The U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE). For the most up-to-date information please visit the EERE website.