Perlite is a lightweight mineral that builders mainly use as loose-fill insulation in masonry. Other uses in insulation include under floors, for fireproofing in areas around chimneys and other locations, and in roof decking and ceiling tiles. As of 2015, studies show perlite to be nontoxic, unlike other materials such as asbestos and fiberglass.
After mining, controlled heating expands perlite ore to as much as 20 times its original size and fills its interior full of tiny bubbles. This makes it a low-density insulator that manufacturers produce in powder, granular and board form. Because granular perlite flows easily into oddly-shaped places, builders use it to fill in the cavities, cores and crevices in masonry walls. Once in place, perlite does not bridge or settle and supports its own weight.
Perlite has a high fire rating and is resistant to vermin, decay, moisture and chemical corrosion. Additionally, it provides sound insulation by muting sound traveling through walls. The U.S. Department of Energy considers it suitable for green building. Although perlite does not match the insulation performance of rockwool or fiberglass, it performs better than loose-fill wood or vermiculite. Builders should not use perlite in areas where it is continuously exposed to temperatures above 200 degrees Fahrenheit.