What’s the Difference Between Cellulose and Fiberglass Insulation?

Choosing which material to use to insulate your home is critical; it could mean the difference of hundreds of dollars in energy bills, not to mention your overall comfort—no one wants to be shivering during a snowstorm. When it comes to insulation materials, two of the most popular choices are cellulose and fiberglass. To help you make an informed decision for your home, let's explore the key distinctions between these two options.

Cellulose vs Fiberglass Insulation: Key Differences

Cellulose is more expensive than fiberglass, however it doesn’t degrade, and its R-value doesn’t lessen in extreme temperatures or when it is compressed. Overall, the R-value of cellulose is higher than that of fiberglass; it will provide better thermal performance than fiberglass. 

R-value, in case you aren’t familiar, is the measurement of an insulation materials’ ability to stop movement of heat. The higher the R-value, the more insulative the material. The R-value of cellulose is typically 3.5 to 3.7 per square inch, while fiberglass offers an R-value of 2.2 to 2.7 per square inch. 

Cellulose, in addition to being more expensive, is also more difficult to install. It must be blown or poured into wall cavities and difficult-to-reach places using special equipment, while fiberglass batts and rolls can be installed without special machinery. 

What Is Cellulose Insulation?​

Cellulose insulation is mostly—75 to 85%—ground-up recycled newspaper and cardboard that has been treated with boric acid, borax, or ammonium sulfate. These chemicals act as flame retardants and help to prevent pest problems. Because the materials used to make cellulose insulation are mostly recycled, it is considered an eco-friendly insulation choice. 

Cellulose insulation comes in two forms: loose-fill and dense packed. Loose-fill is typically used in attics, while dense-packed is used in ceilings and walls.

Best for: 

• Homeowners who wish for an eco-friendly option

• Homeowners concerned about pests

• Insulating around difficult to reach or awkwardly-shaped areas

Pros of Cellulose Insulation

Cellulose insulation is an excellent environmentally-friendly insulation option. Made from recycled organic material, it doesn’t use any greenhouse gasses as propellants, and the additives such as boric acid are excellent at preventing pest infestations. Even though it is more expensive than fiberglass, it is still considered an inexpensive insulation choice. 

Because of the way it is installed (by being blown into the wall cavity), it can conform to a variety of spaces and handles nooks and crannies very well. It has a higher insulation R-value than fiberglass, so it suitable for many more locations and climates than fiberglass.

Cons of Cellulose Insulation

Because cellulose is only available as blown-in insulation, it requires special equipment to install in wall cavities, unfinished attic floors, and other difficult-to-reach places. This installation process can also be messier than that of fiberglass, which comes in neat rolls and panels.

It is also more flammable than fiberglass, even after being treated, and can absorb moisture. After absorbing moisture, it dries very slowly, which can cause it to deteriorate and re-settle. In addition, after installation it settles up to 20%, which can leave gaps in insulation and cause your energy bills to rise unexpectedly. 

What Is Fiberglass Insulation?

Fiberglass insulation has been around since the 1930s, first created by the Owens Corning Company. As the name suggests, fiberglass is made up of very fine glass fibers. It is sold as either batts and rolls, or loose-fill. The batts are sold in different levels of thickness, which correspond to their R-value. 

Best for: 

• Homeowners on a budget

• Those in warmer climates who don’t need a high R-value

• Achieving excellent noise-canceling benefits on top of insulation

Pros of Fiberglass Insulation

Fiberglass insulation is sold in pre-cut panels and rolls, making installation a breeze. Loose fill is also available for special use cases. It is excellent at reducing heat transfer, and does a stellar job at sound-dampening as well. Generally speaking, fiberglass insulation is considered one of the best budget options for insulation.

Cons of Fiberglass Insulation

While a skilled DIY-er can usually install fiberglass insulation on their own, the material is considered hazardous if mishandled or inhaled, so it’s best left to a professional. Fiberglass can also absorb a lot of water when exposed to high levels of moisture, which causes it to lose its R-value. 

Cellulose vs. Fiberglass Insulation

Let’s look a little closer at how cellulose and fiberglass insulation compare to one another so you can make an informed decision about which is right to insulate your home. 

R-Value​: Cellulose

Both materials are considered energy-efficient, but cellulose has an R-value of 3.5 to 3.7 per square inch, while fiberglass offers an R-value of 2.2 to 2.7 per square inch. This means that a thin layer of cellulose can insulate better than the same amount of fiberglass insulation.

Durability​​: Tie

Because cellulose settles up to 20% after installation, you might find that you need to install additional insulation over time, otherwise you might find your energy bills rising. Fiberglass does a better job of retaining its form, can last over 30 years, and often comes with a lifetime warranty. Both insulation types should be examined after 15 years, to check for moisture, pests, and other degradation. 

Price​: Fiberglass

Fiberglass is widely considered one of the most cost-effective insulation options. The cost of fiberglass batt insulation is usually between $0.30 and $1.50 per square foot, but loose fill fiberglass is typically more expensive, running between $1 and $1.50 per square foot. Compare that to cellulose, with costs between $0.60 and $2.30 per square foot.

Ease of Installation/DIYability​: Tie

While both insulation materials are not difficult to install, insulation installation is best left to a local insulation professional who can accurately assess what form of insulation (blown-in, panels, loose-fill) is needed where. In addition, cellulose, while excellent at insulating hard-to-reach areas, does require special machinery for installation which is best handled by a pro.

Eco-Friendliness/Sustainability​: Cellulose

Cellulose is the clear winner here, as it is made up of 75-85% organic, recycled material—mostly old newspapers and cardboard. Fiberglas only contains about 20-30% recycled material.