Homeowners researching insulation often ask: is spray foam insulation flammable? The short answer is yes; spray polyurethane foam is a plastic material that can ignite under the right conditions. But that one-word answer leaves out the most important part of the story. Fire ratings, protective coatings, and proper installation requirements exist precisely because the construction industry recognized this risk decades ago. Understanding those safeguards is what separates informed homeowners from anxious ones.
What Makes Spray Foam a Fire Risk in the First Place?
Spray foam insulation is made from plastic materials that are inherently combustible. When exposed to an open flame or a sustained heat source, both open-cell and closed-cell foam can ignite and contribute to the spread of flames. Untreated foam can also produce toxic smoke, which is a serious concern during a house fire.
That said, modern spray foam products are not raw plastic. Manufacturers add flame retardants and fire retardants during production to reduce the flammability of spray foam insulation and slow fire spread. These additives lower the flame spread index, a measurement used in ASTM E tests to evaluate how quickly flames travel across a material’s surface compared to a baseline. A lower flame spread index means a slower, more manageable spread of fire.
Still, no amount of flame retardants makes spray foam fully fire-resistant on its own. That is why building codes require an additional layer of protection in any space where foam is left exposed.
Learn more about spray foam safety here: Is Spray Foam Insulation Safe? Debunking Common Myths and Concerns
Is Spray Foam Insulation Flammable? The Role of Thermal Barriers and Ignition Barriers
Thermal Barriers
The most common requirement under the International Building Code is that spray foam insulation must be covered by a thermal barrier in occupied spaces. The most widely used thermal barrier is standard drywall. This fire-resistant barrier slows heat transfer from a fire to the foam behind it, buying critical time for occupants to evacuate and for fire suppression systems to respond.
In finished living areas, this requirement is usually met automatically. The walls and ceilings are drywalled, so the foam is never exposed. Problems tend to arise in areas that get overlooked.
Ignition Barriers for Crawl Spaces and Attics
Crawl spaces and attics are high-risk areas specifically because they are often left unfinished. Foam installed in these spaces without proper coverage creates potential fire hazards that would not pass inspection. The International Building Code allows a thinner ignition barrier in limited-access spaces like attics and crawl spaces. Approved materials include certain fire-resistant coatings, fire-rated materials, and specific board products tested to meet safety standards.
Skipping this step is not just a code violation. It is a genuine fire-related risk that can affect your home insurance coverage and your family’s safety.
Open Cell vs. Closed Cell: Does the Type of Foam Matter?
Open-Cell Spray Foam
Open-cell spray foam is softer, more flexible, and less dense than its counterpart. Because it is more porous, it has lower fire resistance properties on its own. It is still treated with flame retardants during manufacturing, but it is generally considered to have less inherent resistance to fire than closed-cell foam. Open-cell foam is a popular choice for interior walls and attic rafters, where it will be covered by drywall or another thermal barrier anyway.
Closed-Cell Spray Foam
Closed-cell spray foam insulation is denser and more rigid. Its compact structure gives it better fire resistance properties compared to open-cell foam, and it also creates a tighter airtight seal that reduces air leakage. For exterior walls, rim joists, and other critical areas in both residential and commercial buildings, closed-cell spray foam insulation is often considered the best option. It delivers superior energy efficiency while carrying stronger fire resistance credentials.
The main difference between the two types of spray foam insulation is not just density. It is the level of protection each provides before a thermal barrier is added.
Learn more about the difference of open-cell vs closed-cell spray foam here: Open Cell vs Closed Cell Spray Foam: A Complete Guide
Fire Codes, Building Codes, and Who Enforces Them
What the Codes Actually Say
Both the International Building Code and local building codes address the flammability of spray foam insulation directly. Requirements vary slightly by jurisdiction, but the core principle is consistent: exposed foam in occupied or accessible spaces must be covered by an approved thermal barrier or ignition barrier. Your local fire marshal and building inspector will check for compliance during inspections.
The National Fire Protection Association also publishes guidelines that influence how spray foam is treated in both residential and commercial settings. Staying current with these safety guidelines is part of what separates a qualified insulation contractor from someone cutting corners.
ASTM E Testing and the Flame Spread Index
The most common fire test referenced in the construction industry is ASTM E84, which measures both the flame spread index and smoke development of insulation materials. Spray foam products are tested against these standards before reaching market. Responsible manufacturers publish their test results, and a qualified insulation contractor should be able to share that documentation on request.
Practical Steps to Reduce Fire Risks
- Always hire a licensed insulation contractor familiar with local building codes
- Confirm that all exposed foam in attics, crawl spaces, and basements is covered with an approved thermal barrier or ignition barrier
- Install and maintain working smoke detectors throughout your home
- Schedule regular inspections of insulated spaces, especially after any renovation work
- Ask your contractor for documentation on the flame spread index and smoke development ratings for the products being installed
The Benefits of Spray Foam Insulation Still Hold Up
Despite its flammability, spray foam remains a top-performing insulation type for a reason. It reduces heat loss, eliminates air leakage, and delivers long-term energy efficiency that traditional insulation often cannot match. When installed correctly with proper fire-rated barriers in place, the potential risks are well managed and the benefits of spray foam insulation speak for themselves.
Peace of mind comes from working with professionals who understand both the performance advantages and the safety requirements.
Ready to Insulate Your Home the Right Way?
At Anthem Insulation, we bring 10 years of experience to every job, and we treat your home like our own. Whether you need spray foam for your attic, crawl space, walls, or a commercial building, our team installs every project to code with the right thermal barriers and fire-resistant materials in place. Contact Anthem Insulation today and let us help you insulate smarter, safer, and with confidence.
