The Ultimate Guide to the Best Thermal Insulation Materials

Thermal insulation is an essential part of making a home more energy efficient, but finding the right material can be a challenge. From bulky fiberglass blankets to futuristic aerogels, there are a myriad of options to choose from. Here's our comprehensive guide to the best thermal insulation materials available.


Fiberglass, which is usually opaque in blocks installed in pieces or rolls, is still one of the most common forms of insulation.

Composed of glass fused and spun into fibers, fiberglass remains one of the most common forms of insulation due to its adaptability, affordability, and effectiveness. Fiberglass can also be presented in the form of loose filling blown with a machine, as well as rigid boards and rolls for ducts. It is resistant to fire and moisture, and much of the material is recyclable. Because of its common characteristics, the mass production of fiberglass has made it one of the most economical options for thermal insulation material, and its adaptive properties make it ideal for DIY projects.

The thermal resistance, or R-value, of fiberglass ranges from 2.2 to 2.7 per inch of thickness, but comparatively speaking, it is low when stacked with other available options. Over time, that value may decrease due to sagging or sedimentation. Fiberglass can be dangerous to install due to its natural properties, as glass chips can become trapped in the skin and cause irritation. If inhaled, it can cause irrefutable damage to the lungs.

Mineral Wool

It's the most ubiquitous option out there when it comes to thermal insulation, but it may not always be the best.

Composed of rock or slag, mineral wool is mainly composed of post-industrial recycled content. Like fiberglass, mineral wool thermal insulation can come in many forms, from rolls and blocks to loose padding, but its R value ranges from 3.0 to 3.3 per inch of thickness. The thermal performance of mineral wool is maintained over time, and its manufacturing process at high temperatures strips it of organic matter, making it a poor environment for moisture and mold. While not as ubiquitous as fiberglass, there are many excellent mineral wool options on the market, including ROCKWOOL, which transforms volcanic rock into a quality rockwool insulator that has been tested for performance and has a high level of use in the residential construction market.


Cellulose thermal insulation material is gaining popularity due to its highly sustainable nature. Made mainly of recycled paper products, reduced to small, fibrous pieces, cellulose usually comes in loose or dense packaging.

It has a typical R-value of 3.2 to 3.8 per inch of thickness and its manufacturing process makes it more affordable. Although naturally more flammable, cellulose can be treated with chemicals such as boric acid to increase its fire resistance, which also makes it less desirable for pests and mold. That said, cellulose is more prone to moisture absorption, so very humid climates might not be the right environment for the material. The additional installation of a vapor barrier will also be necessary, and sagging and sedimentation can also be a problem, as they decrease the R value over time. In any case, cellulose is one of the most sustainable options on the market, and companies like Greenfiber have adopted that concept and have taken steps to help the environment by using lower energy consumption in the manufacturing process.


Styrofoam boards are lightweight and water resistant, and their low water absorption helps prevent mold.

Polystyrene is a versatile material made of clear, colorless thermoplastic. It usually comes in the form of a rigid foam plate; the R-value of this thermal insulation material ranges from 3.6 to 4.0 per inch of thickness; and its foam plate shape makes it easier to install and less dangerous than fiberglass or mineral wool. However, foam boards can be brittle and their initial costs are higher than fiberglass; making them riskier. Its chemical composition is not biodegradable and can create toxins when burned; but its high R value and sound-damping properties make polystyrene an attractive option.Polyurethane FoamPolyurethane foam; more commonly marketed as spray foam; is an insulating material that contains low conductivity gas in its cells. Aerosol foam comes in two types; open cell and closed cell; and the R value depends on the type used.

Closed-cell spray foam typically has an R value of around 6 to 7 per inch of thickness. It works well in climates with high humidity due to its tendency to expand and solidify; making it impervious to moisture. DuPont offers a variety of insulating foams through its Great Stuff product line; one of which is its closed-cell polyurethane spray foam; Froth-Pak. Regardless of the shape; polyurethane spray foam is considered environmentally friendly; as it is one of the most energy efficient insulating materials on the market; with its high R values and its propensity for longevity. Over time; the production of polyurethane foams has been refined to reduce the amount of damage they once caused to the environment; and while a verdict has yet to be reached on their potential health risks; polyurethane spray foam continues to grow as a popular option for energy-saving renovations.Cementitious FoamLike closed-cell polyurethane spray foam; cementitious foam thermal insulation material becomes stiff and solid after being sprayed. While they may not be best for colder environments; cementitious foams are resistant to moisture and mildew; are cost-effective; and can provide additional structural support.


As we enter more innovative territory; aerogel thermal insulation materials are not necessarily new; but their increasing availability has increased their ease of application over the years. Composed generally of silica; aerogels are generally transparent in appearance and have a high gas content that gives them an impressive R value of 10.3 per inch of thickness. This incredible thermal insulation material offers superior protection against heat transfer while being lightweight enough for easy installation.

Perry Holz
Perry Holz

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