Cellulose insulation is not dangerous when properly manufactured and installed. It is one of the most heavily regulated insulation products in the United States, subject to federal safety standards that govern its fire resistance, chemical treatment, and even its potential to corrode metal. That said, there are real risks worth understanding, particularly during installation and in situations where moisture goes unchecked.
What Cellulose Insulation Is Made Of
Cellulose insulation is roughly 80 to 85 percent recycled paper, mostly old newspapers, ground into a dense fiber. The remaining 15 to 20 percent consists of chemical fire retardants, most commonly borate compounds like boric acid and borax. These borates serve triple duty: they resist fire, inhibit mold growth, and deter insects and small rodents. Some products also use ammonium sulfate or ammonium polyphosphate as additional flame retardants.
A common concern about recycled newspaper is whether it contains lead or other heavy metals from old printing inks. Modern newspaper inks are overwhelmingly soy-based or water-based, and the shift away from petroleum-based inks with heavy metal pigments happened decades ago. The cellulose insulation industry uses post-consumer newsprint that reflects these modern formulations.
Fire Risk Is Tightly Regulated
Fire safety was the original reason cellulose insulation attracted federal oversight. The Consumer Product Safety Commission requires all cellulose insulation to have a flame spread rating between 0 and 25 on a standardized 25-foot tunnel test. Every batch must also achieve a critical radiant flux of at least 0.12 watts per square centimeter, meaning it resists igniting even when exposed to significant radiant heat. Products that fail a 14-day corrosion test on copper, aluminum, or steel are banned from sale.
In practical terms, properly treated cellulose insulation chars rather than ignites when exposed to flame, and its dense packing actually slows the spread of fire through wall and attic cavities. The fire retardant chemicals don’t wear off over the product’s lifespan under normal conditions. Problems historically arose with improperly treated batches or homeowner-applied products that skimped on chemical treatment, which is exactly why the federal standards exist.
Dust Exposure During Installation
The most immediate health concern with cellulose insulation is the dust generated during installation. Cellulose dust is classified as a respiratory irritant. OSHA sets a permissible exposure limit of 5 milligrams per cubic meter for the respirable fraction of cellulose dust, the same category as other low-toxicity dusts like titanium dioxide.
Short-term exposure can irritate your lungs, throat, and eyes. Research shows that cellulose dust triggers an acute inflammatory reaction in the lungs that typically resolves after exposure ends, similar to other poorly soluble dusts. This isn’t unique to cellulose insulation. Fiberglass, mineral wool, and spray foam all carry their own installation-phase respiratory risks.
If you’re hiring a professional installer, they should be using dust respirators whenever exposure exceeds the permissible limit. OSHA requires employers to supply appropriate respirators if engineering controls like ventilation aren’t enough to keep dust levels down. If you’re doing it yourself, wear a fitted dust mask rated for fine particles (N95 or better), safety goggles, long sleeves, and gloves. The borate chemicals are low in toxicity for humans at the concentrations used in insulation, but inhaling any fine particulate in large quantities is hard on your respiratory system.
Mold and Moisture
Cellulose insulation is made of paper, so the concern about moisture and mold is intuitive. Here’s the nuance: the borate treatment gives cellulose a genuine advantage over untreated materials. A study testing sodium polyborate-treated cellulose inside wall units at high temperatures and humidity found that the treatment completely prevented the growth of five common mold species for at least 124 days. The borates appeared to have a direct toxic effect on fungal spores, not just slowing growth but killing them.
That protection has limits, though. If cellulose insulation gets saturated from a roof leak, plumbing failure, or chronic condensation from a poorly designed vapor barrier, the borate compounds can leach out over time. Wet cellulose also compresses and loses its insulating value. The material itself isn’t the problem in these cases; the moisture source is. Any insulation type will develop mold issues in a wall cavity with unresolved water intrusion. Cellulose actually handles incidental moisture better than fiberglass because its dense fibers can absorb and release small amounts of water vapor without losing structural integrity.
Indoor Air Quality After Installation
Once installed, cellulose insulation is largely inert in terms of off-gassing. Unlike spray foam insulation, which can release volatile organic compounds during and after application, cellulose is a dry-applied product made from paper and mineral-based fire retardants. The EPA recommends that insulation products meet California’s CDPH Standard Method for testing volatile organic compound emissions, and cellulose products can qualify for GREENGUARD certification under UL 2818, which verifies low chemical emissions.
Boric acid, the primary additive, has very low vapor pressure at room temperature, meaning it doesn’t evaporate into your indoor air under normal conditions. The concern with borates is ingestion or prolonged skin contact at high doses, neither of which applies to insulation sealed inside your walls or attic. In the quantities used in residential insulation, borates pose minimal risk to household occupants.
Pest Resistance
One of cellulose insulation’s genuine benefits is that the borate treatment makes it inhospitable to pests. Boric acid is highly toxic to insects, including cockroaches, termites, and ants. It also deters small rodents. This contrasts with fiberglass insulation, which provides no pest resistance and often becomes nesting material for mice. If you live in an area where pests in wall cavities are a concern, cellulose is one of the better-performing options.
How It Compares to Other Insulation Types
Every insulation material carries trade-offs. Fiberglass releases tiny glass fibers that irritate skin, eyes, and lungs during installation and can become airborne if disturbed later. Spray foam involves isocyanates, chemicals that are genuinely hazardous during application and require supplied-air respirators. Mineral wool dust is a respiratory irritant on par with cellulose.
Cellulose sits in the middle of the risk spectrum. Its installation dust is irritating but not toxic in the way spray foam chemicals are. Its fire performance meets the same federal standards as other insulation types. Its recycled content and borate treatment give it natural advantages against mold and pests that fiberglass lacks. The main vulnerability is water. If you can keep it dry, cellulose insulation is one of the safer and more environmentally benign options available for residential use.