Cellulose vs Fiberglass Insulation

Insulation is essential to help protect your home from outside weather and keep your energy bill from skyrocketing. But not all insulation materials are made equally. 

Each insulation type has its own set of benefits and disadvantages that affect whether or not it’ll fit well with your home. Finding the insulation material that best suits you and your family’s unique needs can make all the difference in creating a safe and comfortable home environment.

To help you figure out which insulation product is best for you, we’re going to be comparing cellulose vs fiberglass insulation. 

The Basics of Fiberglass Insulation

If you’ve seen pink, cloud-like material in attics before, this is not an industrial form of cotton candy—this is traditional fiberglass insulation. Fiberglass is one of the most popular kinds of insulation and for good reason. It’s a low-cost but effective way of regulating the temperature in your home. 

But what is fiberglass exactly? 

Fiberglass is a material made of tiny pieces of mostly recycled material such as glass that has been melted down, combined with other materials like sand and limestone, and then woven into long strands, giving it a cotton-like appearance.

Fiberglass comes in many different forms, but the two that are most commonly used for home insulation are batts and loose-fill fiberglass. 

Fiberglass Batts

Batts are made up of large rolled-up sheets of fiberglass held together by either aluminum foil or adhesive paper.1

Batts are the most commonly used form of fiberglass insulation in homes because they make installation quick and convenient. They’re designed to fit between standard-sized joists, which means all you need to do to install them is to unroll them and then attach them.  

One downside to this type of insulation, though, is that it’s difficult to customize these pre-made rolls to fit different shapes. This makes it hard to install in attics with pipes or other obstructions between joists. 

That’s where loose-fill fiberglass comes in. 

Loose-fill Fiberglass 

Like batts, loose-fill fiberglass is also made up of tiny fibers of recycled glass. Instead of being woven into long blankets, though, they’re cut into small pieces which are then blown into place using an insulation-blowing machine. 

Loose fill insulation allows for people who cannot get batts installed in their attic due to obstructions or other reasons to still be able to enjoy the benefits of fiberglass insulation. 

Pros and Cons of Fiberglass

One of the many reasons fiberglass is a popular choice among homeowners and attic professionals alike is that there are many upsides to fiberglass and only a few downsides.

Advantages of fiberglass include:

  • Cost-Effective – Not only is fiberglass made up of a relatively low-cost material, but it’s also such an effective insulator that it can help decrease your energy bill by 40%, helping you save money in the long run.
  • Long-Lasting – Fiberglass is extremely durable and can last up to 100 years in ideal conditions. Unlike other insulation materials, it also doesn’t shrink over time.
  • Non-Flammable & Moisture-Resistant – Though fiberglass may look like cotton, it’s primarily made up of glass, which means there’s a much lower risk of it catching fire or developing moisture-related problems in humid weather. 
  • Noise Insulation – Fiberglass is an extremely effective insulator not only when it comes to protecting your home against weather, but also against unwanted noise. Whether you live in a busy part of town with lots of traffic or you’ve got a loud generator right outside, fiberglass insulation can help keep your home a quieter and more peaceful place. 

Disadvantages of fiberglass include:

  • Ineffective When Wet – If your fiberglass becomes significantly wet due to a leak in your attic, the insulation will not be able to work effectively until it has been professionally dried. 
  • Self-Installation Can Be Dangerous – Because fiberglass is made up of tiny glass fragments, it can be dangerous to handle it without taking safety precautions and improper handling can lead to health problems like rashes or respiratory damage. That’s why it’s always best to consult an expert while installing fiberglass insulation.

What is Cellulose Insulation?

Cellulose is another popular form of home insulation. It’s typically made from 82-85% recycled material like newspaper or tiny fragments of wood.2 These are then shredded and fiberized so they’ll be able to pack tightly together and stop the flow of heat. 

While there is only one type of cellulose insulation, there are several different ways to install it:

Old Home Installation (Blown Dry)

For homes with a pre-existing structure, part of the siding will have to be removed, a row of holes will be drilled into the wall, and then insulation can be blown in dry.

New Home Installation

  • Damp-sprayed – Moisture is added to the tip of an insulation spray nozzle, activating the starch in the cellulose. It’s then sprayed over the cavities in your home. 
  • Dry-netting – A net is blown full of dry cellulose and then stapled over openings in the building.

The best method of cellulose insulation installation will depend on what kind of home you have and what tools are available to you.

Pros and Cons of Cellulose 

While there are certain advantages of having a paper-based insulation, there are also some notable disadvantages. 

Advantages of cellulose include:

  • Low-price – Because cellulose is primarily made out of paper, it’s an even more inexpensive form of insulation at about 75% of the cost of fiberglass.
  • Easy Installation – Cellulose comes in small pieces and there are many ways to install it, so it fits well with most homes’ structures but can be very messy to install. 

Disadvantages of fiberglass include:

  • Not Pest Repellant Since cellulose is not naturally pest repellant, it’s often treated with chemicals like boric acid that claim to ward off rodents and bugs. In reality, boric acid does little to repel rodents, leaving your home vulnerable to a potential infestation. 
  • Naturally Flammable Cellulose is also treated with chemicals to help make it more flame resistant, but because it’s made of paper, it will always pose more of a fire-risk than a non-flammable insulation material. 
  • Settles After Installation Cellulose insulation tends to settle by several inches after it’s installed, which causes it to decrease in effectiveness. 
  • Mold Grows When Wet Like fiberglass, cellulose is ineffective when wet, but unlike fiberglass, it can also be dangerous. The paper base of cellulose provides the perfect environment for mold and mildews to grow and the boric acid used to treat it can become corrosive when in contact with water.
  • Excess Dust Because cellulose is essentially made up of finely shredded paper, it creates a lot of dust when it’s being installed, which makes it difficult to clean up and can turn it into a breathing hazard for those installing it. 

R-Value: The Role of Thermal Resistance

One of the most important considerations when comparing different types of insulation is R-value. R-value measures the thermal resistance of a material, or in other words, its ability to keep warm places warm and cold places cold. 

Materials with a higher R-value will more effectively insulate your home, helping you keep a more regulated temperature indoors and a lower energy bill. 

Different insulation materials have different ways of combating heat flow and therefore different R-values. Fiberglass’ R-value tends to range between 2.2 and 4.3 depending on the density of the material, whereas for cellulose, the R-value ranges between 3.2 and 3.5. 

This means cellulose insulation has a slightly higher average R-value than fiberglass, but high-quality fiberglass provides better thermal resistance than high-quality cellulose. 

Should I Choose Fiberglass or Cellulose Insulation?

While both fiberglass and cellulose insulation have their own benefits and can be useful in different environments, overall, fiberglass has much more advantages as compared to its downsides.

Fiberglass installation is an affordable, easy-to-install form of insulation that is compatible with most homes and protects against a lot of the dangers caused by poor insulation materials.

Because of this, we recommend fiberglass over cellulose for high-quality insulation that will last. 

Attic Construction: The Experts in Home & Attic Insulation 

Attic Construction is here to help with all your home’s fiberglass insulation needs. Attic Construction is the leading expert in home attic insulation installation and air sealing and is currently rated the number one attic services and insulation company in the San Diego, Orange County, and Phoenix areas.

If you’re not sure where to get started, we offer free insulation consultations to help answer any questions you may have about your home’s insulation. When you request a virtual consultation, you’ll meet with one of our professional contractors for a thorough inspection of your home’s insulation situation and a quote on insulation cost

Visit our website today to sign up for a virtual consultation and start living more comfortably in your home. 


  1. Energy Saver. Insulation Materials. https://www.energy.gov/energysaver/weatherize/insulation/insulation-materials 

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