What is Perlite Insulation?

B. Turner

Perlite insulation is a type of insulation made from volcanic rock. The rocks used to make perlite insulation have a high water content, which helps to create large quantities of air pockets within the rock when heated. These air cells make perlite an excellent insulator, giving it a high level of thermal resistance. In its most basic state, this material has a white chalky appearance and typically comes in the form of small pellets or granules.

Many builders and homeowners rely on perlite insulation to block unwanted airflow in walls, roofs, and foundations.
Many builders and homeowners rely on perlite insulation to block unwanted airflow in walls, roofs, and foundations.

Many builders and homeowners rely on perlite insulation to block unwanted airflow in walls, roofs, and foundations. This material is particularly popular as a form of loose-fill attic insulation. In addition to improving thermal resistance, perlite insulation also blocks unwanted noise to keep the inside of the home quieter. Unlike alternative forms of insulation, perlite also offers a relatively high level of fire resistance, and helps to slow the spread of heat and flames.

Perlite insulation can help prevent issues like mold and mildew.
Perlite insulation can help prevent issues like mold and mildew.

The high thermal resistance of perlite insulation makes it an excellent option for those looking to improve energy efficiency ratings in a home or building. Properly-installed insulation can cut heating and cooling costs and help protect the environment by reducing wasted energy. Effective insulation also improves the overall comfort of occupants and helps to eliminate cold drafts.

Perlite insulation can be found in many forms. Perlite granules may be added to concrete mixtures to improve the insulation of the concrete as it dries. It may also be used as a loose-fill material within the cavities in masonry blocks. Some manufacturers even press perlite into sheets so that it can be used in place of rigid foam insulation in walls or ceilings. Perlite may even be added into the asphalt mixture on a standard asphalt roof to improve insulation and fire resistance.

Outside of the construction industry, perlite insulation is often used in very low-temperature applications. It may be used to line refrigerators for food storage, or to build trucks used for shipping frozen goods. Perlite also serves as a popular insulator in cryogenics and medical research applications.

One of the primary advantages to perlite is its light weight, which allows it to be used in a wide variety of applications. Unlike some other popular insulators, perlite contains only inorganic materials. This means it is resistant to moisture, rot, and even termites and other pests. Perlite's natural moisture resistance eliminates problems with mold and mildew that can often plague other types of insulation.

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Discussion Comments


On what part of the wall, Interior/exterior, your recommended to add extra Perlite insulation?

I have a cavity wall, but the former owner had filled the cavity between the bricks with concrete!


@matthewc23 - I used to work with a company that installed insulation for different projects. I think you the nail on the head. Perlite is a great insulator, but it's best quality is that is forms little beads that you can pour easily. A lot of what we did was use perlite insulation between masonry and things like that.

One of the common uses that you might be able to find for your house is perlite pipe insulation. It works just like the foam stuff you can buy, except it is a lot more effective. We did a lot of work in Minnesota and Wisconsin, and that is what a lot of people wanted to stop their pipes from freezing in the winter.

What I really thought was interesting here was that people use perlite for cryogenics and refrigerators. I guess it makes sense, but I never really thought about using it for anything but building insulation.


@Emilski - I was curious about a lot of the same things as I was reading this. I would be curious to know if someone has more information about perlite.

My best guess would be that, maybe since it is popular in construction, it would end up costing a basic home builder more than ordinary rolled fiberglass or cellulose insulation. The article doesn't say anything really about the ease of installing it in a house outside of the fact that it can be pressed into insulation board.

Maybe getting it into a form that can be blown or easily applied it difficult, so it gets used in cases where the pellets can just be dumped into some other type of mixture.


I am surprised I have never heard of perlite before. I'm not any kind of an insulation expert, but I've done a lot of home improvement stuff, and it seems like I would have stumbled across it at some point.

From reading this article, it also sounds like it is better than fiberglass insulation in almost every way. It is lightweight, can be used in very low temperatures, and is inexpensive, so why isn't it more common in homes, then? I'm sure there has to be more to the story. Instead it sounds like it is mostly used in industrial production like concrete and building construction.

As far as effectiveness goes, how does it compare to something like foam board insulation, and what is the insulation R value?


I remember reading an article about perlite quite a while ago, and it is really interesting how they produce the stuff. It doesn't use recent volcanic material. Instead it is some type of older volcanic rock. Basically, they just mine it somehow and then mix it with water and a couple chemicals and it breaks about into a form that is useable. Also, I remember that most of the production isn't where you think of volcanoes. A lot of it was made in the New England states and Central Europe.

What I never really did figure out from the article was what makes perlite so light? If it is made from volcanic rock, I would expect it to be heavier than most other types of insulation. I would also expect it to me more expensive, but it isn't really.

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