Cellulose insulation is made by shredding recycled newspaper into small pieces, grinding and fiberizing it into fluffy fibers, and then treating those fibers with fire-retardant chemicals like boric acid. The process is straightforward in concept but requires industrial equipment and precise chemical treatment to produce a safe, effective product. Commercial cellulose insulation contains 82% to 85% recycled paper by weight, with the remaining 15% to 20% consisting of fire retardants and mold inhibitors.
Raw Material: Why Newsprint Works Best
The primary ingredient is recycled newsprint. While other paper products like cardboard and office paper can technically be used, newsprint dominates commercial production because its fibers shred and fiberize cleanly, producing the light, fluffy texture that traps air and slows heat transfer. The U.S. Department of Energy notes that cellulose insulation is made from recycled paper products, primarily newsprint.
Newsprint also has relatively consistent fiber quality compared to mixed paper streams. Glossy magazine paper, waxed cardboard, and heavily dyed papers introduce contaminants that can interfere with chemical treatment and reduce insulation performance. Manufacturers typically source baled newsprint from recycling facilities in bulk.
The Four-Stage Manufacturing Process
Turning a stack of old newspapers into insulation involves four distinct mechanical stages, each reducing the material further until it reaches the right fiber size and consistency.
Shredding
The paper first passes through an industrial shredder that tears it into strips and small pieces. This is a rough first pass, not unlike a heavy-duty version of an office paper shredder, designed to break down full sheets and bundles into manageable chunks for the next stage.
Grinding
The shredded material feeds into a hammer mill, a machine that uses rapidly spinning hammers to pulverize the paper into much smaller pieces. The hammer mill is the workhorse of cellulose production, breaking the shredded strips down into a coarse, confetti-like material along with fine dust.
Fiberizing
A fiberizer then takes those small pieces and separates them into individual cellulose fibers and fiber matrices. This is what gives cellulose insulation its characteristic fluffy, cotton-like texture. The fiberizer doesn’t just cut the paper smaller; it pulls apart the paper’s internal fiber structure, creating a material with far more air-trapping capacity than shredded paper alone.
De-Dusting
The grinding and fiberizing stages produce a significant amount of fine cellulose dust mixed in with the usable fibers. A de-duster separates this dust using screening, air classification, or both. Removing the dust is important because excess fines reduce insulation performance and create airborne particulate problems during installation.
Chemical Treatment for Fire and Pest Resistance
Untreated paper fibers burn easily. The chemical treatment stage is what transforms shredded newspaper from a fire hazard into a legitimate building material. Manufacturers add fire retardants and mold inhibitors totaling roughly 15% to 20% of the finished product’s weight.
The most common additives are boric acid and borax (sodium borate). These serve double duty: they make the cellulose resistant to flame and smoldering combustion, and they also inhibit mold growth and deter insects and rodents. Some formulations use ammonium sulfate as an additional or alternative fire retardant. The chemicals are typically applied as a dry powder blended thoroughly with the fibers during or after the fiberizing stage, ensuring even distribution throughout the material.
Getting this ratio right is critical. Too little chemical treatment and the insulation won’t pass fire safety tests. Too much and it can become corrosive to metal fasteners and wiring, or clump when exposed to humidity. Commercial products must meet ASTM C739 standards, which test for corrosiveness, smoldering combustion, critical radiant flux, fungi resistance, moisture absorption, and thermal resistance before the product can be sold.
Why You Can’t Safely Make It at Home
If the process sounds simple enough to replicate in a garage, that’s the dangerous part. The U.S. Consumer Product Safety Commission flagged cellulose insulation safety concerns as far back as 1978, specifically calling out inexperienced manufacturers using poor facilities and inadequate chemical treatment. Fire risks increase significantly with cellulose that is improperly treated with flame retardants.
The core problem is precision. Without laboratory testing equipment, there’s no way to verify that fire retardant chemicals are evenly distributed at the correct concentration throughout the material. A batch that looks and feels identical to commercial insulation could have hot spots with insufficient treatment, sections where the boric acid didn’t penetrate, creating a real fire hazard hidden inside your walls. Commercial manufacturers test every production run against federal flammability standards. A DIY setup has no equivalent quality control.
There’s also the fiberizing challenge. Simply shredding newspaper in a wood chipper or leaf mulcher produces coarse chunks, not the fine individual fibers that give cellulose insulation its thermal performance. Without proper fiberizing equipment, the material won’t achieve the R-value you need, and it will settle dramatically more than professionally manufactured product.
How Cellulose Insulation Performs
Properly manufactured loose-fill cellulose delivers R-3.2 to R-3.8 per inch, according to the Cellulose Insulation Manufacturers Association. That means a 10-inch layer in your attic provides roughly R-32 to R-38 of thermal resistance. For comparison, fiberglass batts typically deliver R-3.1 to R-3.4 per inch, giving cellulose a slight edge at the same thickness.
One factor that affects real-world performance is settling. Loose-fill cellulose compresses under its own weight over time. With proper installation, about 13% settling is normal and expected. Experienced installers account for this by over-filling. If the goal is 17 inches of settled thickness, for example, they’ll blow in about 20 inches initially. Every bag of commercial cellulose includes a table showing installed thickness versus settled thickness to guide this calculation.
Dense-pack cellulose, which is blown into enclosed wall cavities at higher pressure, settles far less because it’s already compressed during installation. It also provides better air sealing than loose-fill, though it requires more material per square foot.
From Factory to Your Walls
The finished product is compressed into bags for shipping and storage. At the job site, the compressed cellulose is loaded into a blowing machine that re-fluffs the fibers and pushes them through a long hose. For attic applications, the installer simply aims the hose and fills the space to the required depth. For walls, a small hole is drilled in each stud bay and the material is blown in under pressure until the cavity is full.
The 80% to 85% recycled content makes cellulose one of the most environmentally friendly insulation options on the market, diverting significant volumes of waste paper from landfills. The manufacturing process itself requires relatively modest energy inputs compared to fiberglass production, which involves melting glass at high temperatures, or spray foam, which relies on petrochemical feedstocks.