Fiberglass is one of the most commonly used insulation materials in residential and commercial buildings. It’s made from glass fibers that are spun into a mat and then bonded with resin. The resulting material is lightweight, strong, and resistant to heat, making it an ideal insulation material.

Fiberglass insulation comes in a variety of forms, including batts and rolls, rigid boards, and loose-fill insulation. It can be used to insulate walls, ceilings, attics, floors, and garages.

Fiberglass insulation effectively reduces energy costs and improves the comfort of your home or business. Here’s an ultimate guide to learning more about fiberglass insulation.

What Types of Fiberglass Insulation Are There?

Fiberglass is made of extremely fine glass fibers. These glass fibers are bundled together to form a strong and flexible material. Different resins may be added to the glass fibers to make the material tougher and more durable.

There are three main types of fiberglass insulation: batts, blown-in, and boards.

Batts and Rolls

Batts and rolls are pre-cut and fit snugly between the studs in your walls. They come in various widths to fit standard-spaced studs. They are made by compressing fibers into a mat and then cutting them to size.

Blanket insulation, or batt and roll insulation, is one of the most common types of fiberglass insulation. It is made from glass fibers spun into a mat and then cut to fit the desired space.

Batt insulation may come with facing or without it. The ones with a facing are called kraft-faced batts and tend to be used in unfinished walls because the facing serves as a vapor barrier.

Fiberglass batts are commonly used in ceilings, ducts, and walls. They’re known to be acoustic insulation, reducing sound transfer between rooms and floors. You can also use them in open walls, the attic, rim joists, and floors.

Cost: On average, fiberglass batts cost $0.64 to $1.19 per square foot. So, if you’re covering a 500-square-foot space, you’ll pay between $300 and $600.


Blown-in fiberglass insulation comprises strands of glass that are pulled to form thin fibers and then sprayed into place with a blowing machine. It can be used to insulate walls, attics, and other areas where it would be difficult to install other types of insulation.

Blown-in insulation is often used in hard-to-reach areas, such as around pipes and electrical wiring.

The R-value of blown-in insulation is 2.2 to 2.7 per inch. That means it’s slightly less effective at insulating than other types of fiberglass insulation.

Cost: The cost of blown-in fiberglass insulation ranges from $1,000 to $1,500 for every 1,000 square feet of wall space.

Fiberglass Boards

Fiberglass boards also constitute molten glass forced through a screen to create long, thin fibers. The fibers are then formed into boards by compressing them with heat and pressure. Up to 60% recycled glass is used in most boards.

Fiberglass boards are used as an insulating material in a variety of applications, including:

  • Attic and crawlspace hatches
  • Ductwork
  • HVAC equipment
  • Pipes
  • Soffits
  • Thermal and acoustic barriers

The installation involves cutting the boards to size and then securing them with adhesive, nails, or screws.

Cost: You can expect to pay $0.30 to $1.50 per square foot of fiberglass board.

Besides these three variants, you can get fiberglass duct tape to seal ductwork and repair HVAC. Since it’s waterproof and flame-resistant, it can be used in high-temperature applications.

What’s Fiberglass R-Value and Thermal Efficiency?

Fiberglass has an R-value of 2.2 to 4.3 per inch. The thermal efficiency increases as the R-value does, which means the form factors of fiberglass with a higher R-value will be better at insulating than those with a lower R-value.

  • Blown-in: R-value 2.2 to 2.7 per inch
  • Batts and Rolls: R-value 3.1 to 3.4 per inch
  • Loose-Fill: R-value 2.2 to 4.3 per inch
  • Boards: R-value 3.1 to 3.4
Insulation Material R-Value 
Fiberglass 2.2 to 4.3 per inch 
Mineral Wool 3.5 to 3.8 per inch 
Spray foam 5 to 7 per inch 
Rigid foam Up to 8 per inch 
Cellulose 3.2 to 3.8 per inch 

Where Is Fiberglass Insulation Most Commonly Used? 

Fiberglass can be used in plenty of applications to help with insulation. It is most commonly used in attics and crawl spaces to keep homes insulated. Here are some residential areas where you can use fiberglass insulation.

House Walls 

Rolls of R-13 or R-15 kraft-faced fiberglass roll insulation are ideal for insulating standard 8-foot walls. To properly insulate, fit the insulation snugly between the studs. Then, staple or tape the paper vapor barrier facing to the studs facing out.


Fiberglass batts are the best form factor for attics since they’re easy to install. You can lay the batts across the floor joists and cut them to fit. You must wear a respirator when handling fiberglass insulation.

Besides energy conservation, fiberglass batts also reduce noise levels and help control condensation.

Between Floors

Use fiberglass boards to insulate between floors in a home. The boards come in different thicknesses and widths, so you can choose the right size for your space. You can choose R2.5 acoustic wall insulation between the floors. R5 to 6 ceiling insulation also works fine.


Fiberglass is one of the best options for insulating the garage from extreme temperatures. You can use faced fiberglass blankets to insulate the walls and ceiling of your garage. As for the garage door, you can choose an insulated garage door or use fiberglass precut batts.


Since faced fiberglass is coated in a vapor barrier, it can lock the moisture out of the basement walls. You can use faced fiberglass batts or blankets to insulate the basement walls (only if the wall has studs). Make sure there are no gaps or voids in the insulation since poorly installed fiberglass insulation can be prone to mold growth.


Fiberglass is one of the most commonly used insulations in crawl spaces. But you should only use it for the first underside of the subfloor. 


Fiberglass batts are the most effective and cost-friendly option for exterior walls if the studs in the walls are the same width as the batt’s thickness. You can insulate the walls by fitting the batts between the studs and joists. Note that fiberglass tends to sag over time, so you’ll need to replace it.

Advantages of Fiberglass Insulation

Fiberglass insulation has many advantages over other types of insulation. Here are some notable benefits.


The national average spray foam insulation cost is between $1,200 and $3,700, which is about $1 to $1.50 per board foot. Meanwhile, fiberglass insulation costs about $0.64 to $1.19 per square foot.

It’s also relatively cheaper than cellulose, which averages $1.20 per square foot.


Fiberglass is mold-resistant since the material itself is not mold’s food source. Some manufacturers also use EPA-approved fungicides to make their fiberglass more mold-resistant.

Meanwhile, other insulation materials, such as cellulose, might attract mold in case of a roof leak or flooding.


Fiberglass does not catch fire due to its glass composition. While it won’t stop a fire from spreading, fiberglass insulation will help to prevent the fire from igniting in the first place. For extra safety, many manufacturers add foils and flame retardants to kraft paper backings.

Meanwhile, the Consumer Product Safety Commission (CPSC) recognizes cellulose insulation as flammable since it’s made of newspaper, a highly combustible material, hence why cellulose insulation is often treated with a fire retardant.

Easy Installation

It’s quite easy to install fiberglass as you only have to cut fiberglass rolls to fit the required space and staple or nail it in place. You can also choose between pre-cut batts or rolls available in different widths.

Some manufacturers also offer easy-to-use, self-adhesive backing that you can simply peel and install. The process is simpler in comparison to spray foam which has to be sprayed using a gun and then left for 24 hours to cure.

Disadvantages of Fiberglass Insulation

Fiberglass insulation has a few disadvantages. Here’s what you should know.

Dangerous When Exposed

Fiberglass insulation is made of tiny glass fibers. These fibers are so small that they can float in the air and get breathed in. When this happens, it can irritate the lungs and cause difficulty breathing. Fiberglass insulation can also cause skin irritation.

The same holds true for spray foam insulation, which has chemicals and cellulose with itch-inducing particles that can irritate skin, lungs, and eyes.

Traps Moisture

Since fiberglass insulation isn’t fully compact, it can trap moisture. This becomes a problem because moisture in fiberglass can lead to mold growth.

Sags Over Time

Fiberglass subsides with age, which creates gaps in your insulation. These gaps allow heat to escape, leading to higher energy bills. Despite that, it still lasts longer than cellulose insulation, with a lifespan of up to 30 years.

What Are Alternatives to Fiberglass Insulation?

Besides fiberglass, there are other materials you can use to insulate different parts of your home. 

  • Rockwool: Rockwool insulation is made from recycled steel slag and basalt rock. It has a higher R-value than fiberglass insulation and is also moisture/mold-resistant. It is commonly used in attics, crawl spaces, and walls. 
  • Cellulose: Cellulose insulation comprises recycled paper products and helps reduce noise travel in residential spaces. It can be used in open new walls, existing walls, unfinished attic floors, etc.
  • Spray Foam: Constitution of two liquid chemicals that expand and harden when mixed, spray foam insulation is perfect for gaps and cracks. It can be used on walls, in attics, under floors, and around pipes. It deters moisture, strengthens buildings, and improves indoor air quality.
  • Denim: Denim insulation is made of recycled jeans and other cotton products. It is a recyclable product used to insulate floors, attics, ceilings, walls, and crawl spaces.
  • Rigid Foam: Rigid foam insulation, compared to fiberglass insulation, provides a more efficient weather-resistant barrier and prevents air leaks, hence making it an ideal alternative ideal for exterior walls, humid environments, and roofs.

Evan has decades of experience as a project manager for large-scale commercial renovation home-building projects throughout the US. Currently, Evan runs a successful construction management company in Virginia.

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