Perlite makes an excellent loose-fill insulator, flowing easily into annulus and odd-shaped spaces—and then staying there. It won’t settle or bridge, won’t rot or attract rodents or termites. It also adds insulative value to anything it’s added to, like concrete or plaster or as a functional filler.
Loose Fill Cryogenic and Low-Temperature Applications
Though there are many concepts for cryogenic and low-temperature storage vessels, the most common feature double-walled construction, with the annular space filled with expanded perlite. Typical examples include helium, hydrogen, and liquefied natural gas containment spheres. Perlite exhibits low thermal conductivity throughout a range of temperatures, pressures, and densities. Expanded perlite is cost effective to purchase and easy to install (either poured or blown into place), is noncombustible, does not shrink, warp, settle or bridge. Perlite is rot and vermin-proof. Many storage systems also incorporate insulating perlite concrete in tank base pads and roofs.
Masonry Loose Fill Insulation
Perlite is an inorganic mineral and is as permanent as the block walls it insulates. Perlite’s expanded, mineral-foam nature means it is an excellent insulator. It supports its own weight and will not settle or bridge. Hollow core masonry walls can be inexpensively filled with loose perlite—poured directly from the bag. Perlite insulation improves the heat transmission of that block wall by 50% or more. Perlite has been used for this purpose for decades and ASTM testing specifications, test results, and thermal design tables are readily available. As for perlite's acoustical properties, lightweight 8 in. (20 cm) masonry block filled with expanded perlite achieves an STC of 51, which exceeds HUD sound transmission standards.
In a unique application of expanded perlite’s insulative properties, unopened perlite bags are placed under concrete slabs to provide a thermal break between soil and concrete and mitigate heat loss—of particular benefit to radiant in-floor heating systems. Expanded perlite is dimensionally stable, non-combustible, and will not rot. For more information, download the Perlite Institute publication linked below.
In simple applications like rocket stoves or pizza ovens—whether poured loose into a cavity space or used to make a lightweight cement—perlite provides resistance to thermal transfer. For example, the fire rating on a typical concrete block wall is doubled—from 2 hours to 4 hours—when the block cores are filled with perlite. (See UL Designs U901, U904, U905, and U907.)
In foundry applications, expanded perlite is used as an insulative cover over molten metals, mitigating heat loss. Perlite is mixed with exothermic powders and used to prevent shrinkage cavities in ingots and castings. Perlite is added to foundry core and molding sand mixtures to cushion and compensate for expansion during phase change, minimizing casting defects.
Other applications include fire-rated door cores, insulation boards, pipe and duct insulation, ceiling tiles, and concrete roof decks.
Spray-Applied, Fire-Resistant Materials (SFRMs)
Expanded perlite makes an ideal non-combustible (per ASTM E136), inorganic aggregate filler for sprayed-on fire protection coatings and plasters. Such spray-applied, fire-resistant materials are typically used to insulate structural steel to prevent failure that might result from rapidly rising temperatures. Perlite particles are extremely lightweight, frothy mineral bubble clusters that are readily compatible with cementitious and other SFRM formulations. Having been flash-expanded from its graded, raw ore form at high temperature, perlite can withstand temperatures from 1600 to 2000ºF before reaching its softening point. The fusion point is 2300 to 2450ºF.
The various available expanded grades provide particle size options to best fit the carrier and the application, with gradation (particle size) having only a minor effect on the insulative value. Perlite has been used for insulative, fire-resistant plasters and spray-on cementitious coatings since the 1940s, with well-documented results and proven mix designs. Performance specifics depend greatly on the design, installation, and the materials used.
Applications include interior structural steel framing such as columns, beams, and girders, steel decking for floors and roofs, and cementitious spray-and-trowel plaster for walls and ceilings.
Insulative Perlite Concrete
Expanded perlite, when used as an aggregate in concrete, imparts insulative properties to the concrete—properties that are extremely useful for fire-retardant plasters, insulating concrete cores in chimneys, specialty stoves, ovens, doors, furnaces. For more information, visit the page on lightweight perlite concrete.