Most types of foam are flammable, and some are dangerously so. Polyurethane foam, the material found in couch cushions, mattresses, and car seats, has a limiting oxygen index of around 18%, meaning it ignites easily in normal air and burns rapidly once lit. The specific risk depends on the type of foam, whether it contains flame retardants, and how it’s used.
Why Polyurethane Foam Burns So Easily
Polyurethane foam is the most common foam in household products, and it’s one of the most flammable materials in a typical home. Its open-cell structure gives it a high surface-area-to-volume ratio, which means fire can spread through it quickly. Once ignited, it burns with intense heat. In lab testing, untreated rigid polyurethane foam reaches peak heat release rates around 90 kilowatts per square meter and can ignite in as little as 13 seconds when exposed to a radiant heat source.
The cellular structure that makes foam lightweight and comfortable also makes it an efficient fuel. Air trapped inside the cells feeds the combustion process, and the thin walls of each cell break down rapidly under heat. A single couch cushion made of untreated polyurethane foam can become fully engulfed in under a minute.
Toxic Gases From Burning Foam
The flames themselves are only part of the danger. When polyurethane foam burns, it releases a cocktail of toxic gases: carbon monoxide, carbon dioxide, hydrogen cyanide, nitrogen dioxide, and ammonia. Hydrogen cyanide and nitrogen oxides are particularly dangerous because they act as asphyxiants, interfering with your body’s ability to use oxygen even if you’re still breathing. In fire fatalities involving upholstered furniture, smoke inhalation from these gases is often the cause of death, not the burns.
Lab measurements of burning polyurethane show total toxic gas concentrations above 250 grams per cubic meter, with carbon monoxide and carbon dioxide making up the bulk of emissions. Even in small quantities, hydrogen cyanide (measured at roughly 2 grams per cubic meter in testing) can be lethal with brief exposure in an enclosed room.
Foam Insulation and Building Codes
Spray foam insulation, rigid foam board, and extruded polystyrene (XPS) are all foam plastics used in construction, and all of them are inherently flammable before treatment. Building codes account for this. The International Building Code requires foam plastic insulation to have a flame spread index below 75 and a smoke developed index below 450 when tested under the ASTM E84 tunnel test. For exterior walls, the requirements are stricter: a flame spread index below 25.
Commercial insulation products are formulated to meet these thresholds. XPS insulation boards typically test with flame spread indexes between 0 and 15, well within code limits. Spray polyurethane foam insulation products generally test below 25 for flame spread. But these ratings apply to the product as manufactured with flame retardants. If the retardant chemicals degrade over time, or if the foam is used outside its tested conditions (applied too thickly, for example), fire performance can change.
Building codes also require that foam insulation be covered with a thermal barrier, typically half-inch drywall, to slow fire exposure. Exposed spray foam in an attic or crawl space that hasn’t been covered with a barrier is a code violation in most jurisdictions.
How Flame Retardants Work
Flame retardants are added to foam to slow ignition and reduce the intensity of burning. They work through two main strategies. Some release compounds into the air during heating that interrupt the chemical reactions of combustion, essentially starving the flame of the reactive molecules it needs. Others form a protective char layer on the foam’s surface that acts as a physical barrier, blocking oxygen and heat from reaching the unburned material underneath.
Expandable graphite is one of the more effective additives. When heated, it swells into a dense, highly graphitized carbon layer that insulates the foam beneath and suppresses both heat and smoke release. Phosphorus-based retardants work in both phases: some of the phosphorus vaporizes and disrupts gas-phase combustion, while the rest catalyzes the formation of a stable carbon char on the surface. Combining these approaches can reduce peak heat release by roughly 19% and meaningfully lower smoke production.
Flame retardants don’t make foam fireproof. They buy time, slowing ignition and the rate of fire growth so that occupants have more seconds to escape and detectors have more time to activate.
Furniture Foam and Safety Standards
Upholstered furniture is one of the leading contributors to home fire deaths in the United States. Since June 2021, all upholstered furniture manufactured, imported, or reupholstered in the U.S. must comply with California Technical Bulletin 117-2013, a federal requirement codified by the Consumer Product Safety Commission. This standard tests cover fabrics, filling materials, and barrier materials for smolder resistance, meaning resistance to slow, cigarette-type ignition sources.
TB 117-2013 replaced an older standard that focused on open-flame resistance and effectively required large amounts of chemical flame retardants in furniture foam. The newer standard shifted to smolder testing, which reduced the need for added chemicals while still addressing the most common ignition source for furniture fires. If your furniture was made before 2021, it may contain older-generation flame retardants, some of which have raised health concerns over long-term chemical exposure.
Styrofoam and Polystyrene
Expanded polystyrene (EPS), commonly called Styrofoam, is also flammable. It’s a petroleum-based plastic foam that melts at relatively low temperatures and ignites readily. When burning, it produces thick black smoke and can release styrene gas. Polystyrene foam cups, coolers, and packaging materials will catch fire from a direct flame and burn aggressively, with melting droplets that can spread fire to other surfaces. Insulation-grade polystyrene is treated with flame retardants, but the disposable consumer products generally are not.
Foams That Don’t Burn
Not every product called “foam” is flammable. Firefighting foams, for instance, are water-based solutions mixed with surfactants that create a blanket of bubbles designed to smother fuel fires. These foams are non-combustible by design. Aqueous film-forming foams have been used since the 1970s for liquid fuel fires, though their traditional formulations containing PFAS chemicals are being phased out due to environmental and health concerns. Fluorine-free alternatives are replacing them.
Melamine foam, the material in cleaning erasers, has naturally low flammability compared to polyurethane. Ceramic and glass foams used in industrial applications are essentially non-combustible. But when most people ask whether foam is flammable, they’re asking about the soft, spongy material in their furniture, mattress, or walls. That foam is almost always polyurethane or polystyrene, and the answer is yes, it burns readily and dangerously.