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What is Perlite?

Thermal Design- Concrete Masonry Wall

Thermal Resistance Calculations

Perlite Masonry Block Loose-Fill Coverage

Perlite Loose-Fill Insulation Guide Specification

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Perlite Loose-Fill Insulation

Perlite loose fill insulation is an inert volcanic glass expanded by a special heat process that can be treated with water repellent material when necessary. The resulting granular product is lightweight with countless tiny, sealed air cells, which account for its excellent thermal performance and fire resistance.

Perlite insulation has been proven over a period of many years in the insulation of storage tanks for liquid gases at temperatures as low as 400 degrees Fahrenheit (-240 Celsius)


Reductions in heat transmission of masonry walls of 50% or more may be obtained with perlite loose-fill insulation.  Thermal performance tests using ASTM C236, Test Method for Steady State Performance of Building Assemblies by Means of a Guarded Hot Box have shown perlite to be a superior concrete block insulation when compared to vermiculite, EPS inserts, EPS beads, and foamed-in-place insulation's.

Recent testing of an 8 inch medium weight concrete block wall filled with perlite loose-fill insulation using dynamic conditions simulated by a National Bureau of Standards 24 hour (diurnal) test cycle indicates that the measured total energy (total heat flow through a wall for a 24 hour period) was only 72 percent of the total energy predicted by steady-state analysis.

Non-Combustible--The fusion point of perlite is 2300 degrees Fahrenheit (1260 C)

--Flame Spread 0, Fuel Contribution 0, Smoke Density 0.

--Critical Radiant Flux greater than 1.07 Watts/cm2
.  Smoldering Combustion, Flaming Combustion - None, Weight  Loss-Nil.

4 Hour Fire Ratings--Underwriters' Laboratories Design No. U905 shows that a 2 hour rated 8, 10, 12 inch (20, 25, or 30 cm) concrete block wall is improved to four hours when cores are filled with water repellent treated perlite.  U.L. Designs U901, U904, and U907 also achieve 4 hour fire ratings.

Permanent--Perlite is an inorganic, naturally occurring mineral and it is as permanent as the walls which contain it.  It supports its own weight and will not settle or bridge.

Water Repellent--Perlite loose fill insulation can be treated to minimize water transmission. Laboratory tests on water transmission by Structural Clay Products Research Foundation showed a cavity wall filled with treated perlite resists transmission of water to the interior wythe even under the most severe conditions. Performance of overall wall was rated "excellent" in accordance with procedures established by the National Bureau of Standards in BMS 82. However, it should be noted that treated perlite insulation will not waterproof a poorly constructed masonry wall.  Good construction practice should also incorporate the use of weep holes covered with copper, galvanized steel, or fiberglass screening.

Sound Reduction--Perlite loose fill insulation has the ability to fill all voids, mortar lines, and ear holes thus enabling it to reduce airborne sound transmission through walls. Lightweight 8 inch (20 cm) masonry block filled with perlite achieves an STC of approximately 51 which exceeds HUD sound transmission standards.

Economical--Perlite loose-fill masonry insulation offers excellent thermal and fire resistant properties at an economical cost.  It is lightweight and pours easily and quickly without requiring special equipment or skills.


  • ASTM Specification C549 for Perlite Loose Fill Insulation
  • ASTM Specification C520 Density of Granular Loose Fill Insulation
  • ASTM Specification C236 Test Method for Steady-State Thermal
  • Performance of Building Assemblies by Means of a Guarded Hot Box
  • ASTM Specification E84 Test for Surface Burning Characteristics of Building Materials
  • FHA Use of Materials Bulletin UM-37
  • GSA Commercial Item Description A-A-903 Insulation, Thermal(Expanded Perlite)
  • Brick Institute of America Technical Notes No 21A
  • Federal Specification HH-I-515D

Information given herein is from sources considered reliable, but no guarantee of accuracy can be made or liability assumed.  Your supplier may be able to provide you with more precise data.  Certain compositions or processes involving perlite may be the subject of patents.
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