What is Perlite Insulation?

Perlite is a type of insulation manufactured from siliceous lava–sometimes called volcanic glass. The rock contains up to 6% water and when heated will expand up to 20 times its original size. It pops somewhat like popcorn and traps air inside the resulting product. The result is insulation with an R-value of R-2.7. Perlite is not a brand name; but the name of the rock and of the manufactured material.

Perlite Insulation

Why Perlite Works

During the manufacturing process, the lava is heated to 1700 degrees F. As the water pops out it creates millions of microscopic glass air bubbles in each small clump of perlite. Air is the insulator. The resulting product is small enough to completely fill and seal construction cavities.

The free-flowing product is ideal for pouring into odd-shaped cavities. Or cavities like concrete block walls with masonry protrusions and voids. It also flows easily around electrical boxes and framing in attics and wall cavities.


Perlite is a non-renewable resource but the estimated world reserve is around 700 million tonnes. World production is about 5 million tonnes per year. Some of the benefits of using perlite for insulation include:

  • Inorganic. Contains no plant or animal additives.
  • Non-combustible. Does not burn and slows flame spread.
  • Loose Flowing. Easily flows into and fills small cavities.
  • Pest Resistant. Not a food source for rodents or insects. Highly resistant to mold and mildew.
  • Green. Considered an eco-friendly insulation because it contains no chemical additives. None are used during the manufacturing process.
  • Inexpensive. Less than $15.00 per 4 cubic foot bag.


Perlite insulation has some disadvantages that restrict its use as insulation.

  • R-value. R-2.7 is lower than many competing types of insulation.
  • Fragility. Transportation or improper handling can turn it into dust.
  • Dusty. Respirator, glasses, and gloves are recommended when handling.
  • Shrinkage. Prone to caking when wet. Wet perlite can shrink up to 10%.

Perlite, Vermiculite, and Asbestos

Perlite is often confused with vermiculite insulation. Much of the vermiculite used in North America was contaminated with asbestos. Perlite contains no asbestos. Processed perlite is almost pure white after processing and emerges as small granules. Vermiculite is beige or brown.

If in doubt, test kits are available online or from laboratories that test for asbestos. Take a sample of the insulation and send it away for analysis.

Uses of Perlite Insulation

The properties of perlite make it an ideal insulation material for a wide range of applications.

  • Attics. Loose-fill attic insulation can be poured in place.
  • Concrete Blocks. Reduces heat transmission of concrete block walls by up to 50%. Can also be poured into double-wall brick construction.
  • Rigid Insulation Boards. Pressed into sheets–sometimes combined with gypsum–it can be used to replace rigid foam insulation.
  • Fire-rated Doors. Provides fire-rated insulation door cores.
  • Roofing Boards. Fireproof cover boards.
  • Pipe Wrap. Fireproof pipe wrapping.
  • Cryogenics. Insulates double-walled containers holding super-cold products like hydrogen and helium.
  • High Temperature. Applications such as pizza ovens and double-walled chimneys.
  • Concrete. Under concrete slabs preventing heat loss into the soil.
  • Acoustics. Absorbs sound in studio walls and ceilings.