What is the R-Value of Fiberglass Insulation?

You are in the market for some new insulation for your home. You’ve heard a lot about fiberglass insulation and its r-value, but you’re not sure what it means or how it affects you. You decide to do some research to learn more.

Fiberglass insulation is a popular choice for homeowners because it is relatively affordable and can be installed in various ways. It also has a good r-value, meaning it can help to keep your home warm in the winter and cool in the summer. Fiberglass insulation may vary slightly by the manufacturer, but typically it has an R-value between 2.5 to 4.3 per inch.

What is Fiberglass Insulation Made of?

Fiberglass insulation is made of tiny glass fibers mixed with resin and formed into batts or blankets. The glass fibers are very thin, which allows them to trap air and create an insulating layer. The resin holds the fibers together and helps to prevent them from settling over time.

Fiberglass Insulation

Types of Fiberglass Insulations

There are three different types of insulations on the market. There are a few different types of fiberglass insulation on the market.

  • Unfaced fiberglass is made of glass fibers that are not coated with a resin. It is usually used in attics and crawl spaces, which can be used between rafters or joists. Unfaced fiberglass insulation is not as effective as other types of insulation at preventing air infiltration, but it is the most affordable option.
  • Faced fiberglass is made of glass fibers that are coated with a resin. This type of insulation is usually used in walls and ceilings and can be used between the studs or panels. Faced fiberglass insulation is more effective than unfaced insulation at preventing air infiltration and has a higher R-value. However, it is more expensive than unfaced insulation.
  • Blown-in fiberglass is made of tiny fibers blown into tight spaces in the attic or wall cavity using a special machine. Blown-in insulation prevents air infiltration and can be used in attics, walls, and ceilings. You can get the best coverage when insulating an attic or wall cavity by blowing the insulation in with pneumatic equipment.

Why R-Value is Important with Fiberglass Insulation?

When it comes to insulation, the R-value is one of the most important factors to consider because the R-value of an insulating material indicates how efficiently it prevents heat transfer. The higher the R-value, the better the insulation will prevent heat loss.

Fiberglass insulation R-values can vary slightly depending on the manufacturer, so it’s best to consult with the specific manufacturer to get an accurate R-value. However, R-values for fiberglass insulation are typically listed in the product’s technical specifications.

How to Calculate the R-value of Fiberglass Insulation?

R-values per inch of thickness are what you need to compare when evaluating the thermal resistance of different insulating materials. The following insulation thickness chart (R-value chart) helps you to understand Fiberglass R-values based on insulation type with different thicknesses per inch.

Type of Fiberglass InsulationPer Inch4 Inch Thickness6-inch Thickness8-inch Thickness
Fiberglass BattsR-3.7R-14.8R-22.2R-29.6
High-Density Fiberglass BattsR-4.3R-17.2R-25.8R-34.4
Loose-Fill FiberglassR-3.1R-12.4R-18.6R-24.8
Rigid Panel FiberglassR-2.5R-10R-15R-20
R-value of Fiberglass Insulation

How to Calculate the Highest R-Value for a 2×4 Wall?

With the help of the above R-value calculation chart. A 2×4 wall cavity can be insulated with R-13 or R-15 fiberglass batts. R-15 is the highest R-value you can use on a 2×4 wall.

What is the Fiberglass Insulation R-Value for a 2×6 Wall?

By using a 6-inch fiberglass batt with an average thickness of 3.5 inches, you may use up to R-21. Alternatively, on a 2×6 wall, you can use fiberglass batts in the R-13, R-15, and R-19 ranges.

Is Fiberglass a Good Insulation?

It is becoming increasingly popular as a way to insulate homes and businesses. It is made of glass fibers bonded together with resin and has a relatively long lifespan.

What are the Advantages of Fiberglass Insulation?

There are several benefits to using fiberglass insulation in your home. Some of the key benefits include:

  • Fiberglass insulation has a high r-value, meaning it is effective at preventing heat loss. It keeps your home warm in the winter and cools in the summer. It helps to regulate the temperature in your home in an energy-efficient way.
  • Fiberglass insulation is made of glass fibers bonded together with a resin. The fibers are typically tiny, with a diameter of around 0.00005 to 0.0002 inches. This makes the insulation very lightweight and durable.
  • It is affordable compared to other different insulation materials (cellulose insulation, spray foam insulation) in the market and can be easily installed in various ways.

What are the Disadvantages of Fiberglass Insulation?

While fiberglass insulation does have several advantages, there are also a few disadvantages to consider before deciding if it is the right choice for your home.

  • Fiberglass insulation can cause respiratory problems if it is not installed correctly. If the fibers are disturbed, they can become airborne, and inhalation can cause health problems. It is essential to ensure the installation is done by a qualified professional to avoid any health risks.
  • Fiberglass can absorb moisture. If there is a lot of water in the air, the insulation can become saturated and will not be as effective at preventing heat loss.

Where can you Use Fiberglass Insulation?

Fiberglass insulation can be installed in various places in your home, depending on your needs. Some of the most common places to install fiberglass insulation include:

Installing Fiberglass Insulation


Fiberglass insulation is an excellent choice for attic insulation because it can help to keep the attic cool in the summer and warm in the winter. Radiant barriers are often installed on the underside of the roof to reduce the radiant heat flow. However, they can increase the thermal resistance of the insulation by an additional R-2 when placed over existing insulation on the attic floor.

In the north, R-49 insulation thickness is often used in attics, but when it comes to warmer climates, insulation thicknesses of R-30 and R-19 are the most popular.


In colder climates, the basement is a crucial area to insulate to keep the home warm. It is a good choice because it has a high R-value and can help keep the basement insulated and comfortable.

Fiberglass insulation


Installing fiberglass insulation in your walls can help to prevent heat loss and save you money on your energy bills. However, wall insulation depends on what kind of framing is used. Different materials offer higher or lower R-values, but the width of the studs still limits wall insulation.

If the walls are made of 2x4s, you can use rolled fiberglass insulation with an R-11 to R-15 value. If the walls are made of 2x6s, you can use between R-19 and R-21.

Ceiling Fiberglass Insulation


The ceilings of your home are another critical area to consider when installing fiberglass insulation. Installing fiberglass in your ceilings can help to regulate the temperature in your home and keep it comfortable year-round.

In the summer, installing fiberglass in your ceilings can help to keep the ceiling cool, and in the winter, it can help to keep the ceiling warm. This is because fiberglass insulation has a high R-value, meaning it is effective at preventing heat loss.

How to Install Fiberglass Insulation?

Installing fiberglass insulation is a relatively straightforward process that most homeowners can do. Here are the basic steps:

Measure the Fiberglass Insulation
  • Measure the area you want to insulate and purchase the appropriate fiberglass insulation. Make sure to purchase enough insulation to cover the entire area you want to insulate.
  • Cut the insulation to fit the size of the area you are insulating. Cutting it to measure can be difficult, so it’s best to purchase it in the correct size.
  • Use a staple gun or duct tape when attaching the insulation to the wall or ceiling. Be sure to seal all gaps and cracks properly to prevent heat loss.
  • To reduce exposure, dress in long sleeves, work gloves, protective eyewear, trousers, and a face mask. 
  • Make sure all gaps and cracks are correctly sealed to prevent heat loss.

If you are unsure how to install fiberglass by yourself and to make make sure of a proper installation, it is best to consult with a professional insulation contractor.

What are the Alternatives to Fiberglass Insulation?

There are a few other insulation alternatives to fiberglass insulation, including:

Cellulose Insulation: made of recycled paper products, cellulose insulation is a good option for those looking for an environmentally-friendly choice. It is also effective in preventing heat loss. The average cellulose insulation R-value is ranging R-3.4 to R-3.8 per inch.

Foam Insulation: foam insulation is sprayed onto surfaces and can be a good option for insulating tight spaces. It is also effective in preventing heat loss.

Open Cell Spray Foam

There are two types of spray foam insulations.

  • Open cell foam spray insulation comprises tiny cells filled with air. This type of insulation is less expensive than closed-cell spray foam insulation but less effective in preventing heat loss.
  • Closed-cell spray insulation comprises tiny cells filled with gas twice as dense as air. This type of insulation is more expensive but more effective in preventing heat loss.

Rigid Foam Insulation: made of polystyrene or polyurethane, rigid foam insulation is a good choice for insulating an attic or basement.