A Survey of Fire Rated Insulation Types

Insulation between studs

When you're trying to stay warm over the winter, there are typically two routes you can take - crank up the heat and increase the insulation of your structure. But with the nearly 1.3 million fires reported every year, how do you protect yourself against your insulation from catching fire? By using fire rated insulation. In this post, we'll take a solid look at different types of fire rated insulation and what situations they perform best.

Mineral Wool

One of the most recognized fire rated insulation types, mineral wool is quite possibly the very best in fire resistant insulation. Also called slag wool or rock wool, mineral wool is created from noncombustible fibers. It's able to withstand heat up to 1,800ºF, much higher than the average home fire's temperature of 1,100ºF.

Spray Foam

Spary Foam Insulation

Because spray foam itself is flammable, virtually all spray foams sold in the US contain fire retardants. Because it fills the cavity completely, it provides no additional air or channels for the fire to spread to other parts of the structure. That being said, an installer who doesn't know their stuff can actually cause a fire when spraying in the installation. Take, for example, a new firefighter who was helping his wife prepare their rental home for winter by applying canned spray foam directly underneath the gas water heater. Did we mention that the water heater had a lit pilot? You would think that he should have known better, but now all the neighbors know exactly how girly even an ex-Navy SEAL's screams can be when trying to exit a short crawl space with all due haste.


Fiberglass is, by definition, fine fibers of glass. This means that it won't burn unless you have a situation significantly higher than the average house fire. Glass has a boiling point around the same as mineral wool, but the fine texture of the fibers means that it has more surface area exposed, so though it will withstand a house fire, it would still melt before mineral wool would. Fiberglass insulation also leaves gaps around wires, pipes and other obstructions inserted into the wall, which can leave a channel along which fire can spread.

Cellulose Blown In Insulation


Because of the way cellulose is blown in, it can do a better job of filling a wall cavity around electrical boxes, wires and pipes, especially when compared to fiberglass, which can leave gaps where fire can spread. That being said, it's important to make sure that the cellulose insulation you're using has been treated with a fire retardant. One popular option for those who prefer green living is cellulose treated with boric acid, a natural substance that has the bonus of driving insect pests away.

Electrical Box Insulation

Though this is a very small area of insulation, drafts from electrical boxes can be a serious problem for air leakage. At the same time, electrical fires is a major cause of fires in the United States. Rather than using the cheap foam insulation you can buy in any home store, invest in electrical box insulation that also suppresses fire, helping to increase your home's fire safety.

Foam Board

Though it's easy to install, foam board isn't fire resistant unless you've installed a minimum of 1/2" of drywall over the top for interior installations. It can also release toxic vapors when burning, so if you're considering installing it in your home, you may want to consider options to improve its resistance to catching fire.

Knowing the best type of insulation for your project is vital to maximizing your energy efficiency, but using fire rated insulation provides the best protection against accidental fires. At Wallboard Supply Company, we're happy to help you find the perfect fire rated insulation for your job.

PS - If you need more information on insulation products we carry, including LEED Certified Insulation options, download our free product guide below.

LEED Certified Building Insulation Product Guide

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Wallboard Supply Company is a third generation, family run business that has been serving New England's building needs since 1970. Bob Filion started the company with a commitment to provide quality drywall and finishing products with unmatched customer service. The company has grown over the years, expanding its' product range, but never wavering from its' core values.