by Nick Gromicko and Rob London

Perlite is a naturally occurring siliceous rock used for thermal insulation in buildings. 

Production

The United States is the world's largest producer and consumer of perlite. Other leading countries that produce perlite include China, Greece, Japan, Hungary, Armenia, Italy, Mexico, the Philippines, and Turkey. You may recognize it as the small white pebbles used in potting soil to improve aeration and moisture retention. 

After it is mined, perlite is heated to approximately 1,600° F (871° C), which causes its water content to vaporize and create the myriad tiny bubbles that account for the mineral’s unique physical properties. Perlite insulation is produced in a granular form as well as a powder form, but some manufacturers combine it with gypsum or other materials to turn it into an insulating board. In addition to its use as an insulator in buildings, perlite is used for the insulation of low-temperature equipment, such as super-cold storage and cryogenic tanks, as well as in food-processing applications.

Physical Properties and Identification

Insulation found in homes may be made of perlite if it possesses the following qualities:

• it is snowy white to grayish-white in color. The crude rock ranges from transparent light gray to glossy black, but the expanded form found in homes is easily identified by its white color;
• it is lightweight. Expanded perlite can be manufactured to weigh as little as 2 pounds per cubic foot; and/or
• its’ grain sizes may vary, but they generally are not larger than ¼-inch in diameter.

Perlite's Performance as an Insulator

Perlite is widely used as loose-fill insulation, especially in masonry construction, because of the following qualities that make it desirable:

• low toxicity. According to the Perlite Institute, “No test result or information indicates that perlite poses any health risk.” Other insulators, such as asbestos, vermiculite (which may contain asbestos), and fiberglass are more hazardous;
• chemical inertness, meaning it will not corrode piping, electrical or communications conduits. Perlite has a pH of around 7, which is similar to fresh water;
• pliability. As a loose-fill insulator in masonry construction, perlite can be poured into the cavities of concrete block where it completely fills all crevices, cores, mortar areas and ear holes. The mineral will flow around any roughness, unevenness or exposed installations. It supports its own weight and will not settle or bridge;