Definition of perlite in US English:



  • A form of obsidian characterized by spherlulites formed by cracking of the volcanic glass during cooling, used as insulation or in plant growth media.

    • ‘With hot adhesives, however, it has to be paired with an insulation cover board of another type, such as perlite or wood fiber.’
    • ‘These soil mixtures should include sand, peat moss, perlite, vermiculite, and fir bark for adequate drainage.’
    • ‘The mix we use contains compost, peat, perlite, rock phosphates, blood meal, calcite clay and gypsum.’
    • ‘Use a premixed potting soil, usually composed of sand, peat moss, fine bark, perlite or vermiculite.’
    • ‘Most soil-less mixes are a combination of peat, perlite & vermiculite and drain very quickly.’


Mid 19th century: from French, from perle ‘pearl’.