A split image with a man on the left side spraying spray foam insulation, and a person on the right side installing fiberglass insulation batts.

Insulation is crucial for keeping your home comfortable and energy-efficient. There are several insulation options, but fiberglass and spray foam have become increasingly popular. So, what sets them apart?

Spray foam insulation has a higher R-value than fiberglass, making it a better insulator. Another difference between them is that spray foam is watertight while fiberglass cracks under moisture. However, installing spray foam requires a professional while fiberglass is easy to install yourself.

Are you unsure of which insulation to use between fiberglass and spray foam for insulation? Read on for detailed explanations of their differences, pros, and cons to make an informed decision.

A Head-to-Head Comparison of Fiberglass and Spray Foam Insulation

Your choice of insulation material makes a significant difference in the energy efficiency of a home. Plus, it affects indoor air quality, depending on the substances a given insulation type produces, so you want to ensure you choose carefully. 

Therefore, there are many factors to consider when making this decision.

To decide between the most popular choices: fiberglass and spray foam, you should consider their R-Value, cost-effectiveness, resistance to moisture, durability, ease of installation, and health effects.  

It’s also important to note that fiberglass insulation comes in two categories:

  • Batts – blanket-style insulation that can be cut to size and stuffed into a wall cavity.
  • Loose-fill – loose fiberglass pieces that look like pillow stuffing that gets blown into the wall cavity once it’s been covered with a protective layer mesh fabric.

Let’s take a look at these in more detail below.

Batt Style Fiberglass Insulation

As the name suggests, fiberglass insulation is made up of fine strands of glass. 

Batt, or blanket, insulation uses spun molten glass that gets layered on a conveyor belt. Eventually, it becomes thick enough that it can be rolled up for use in your home.

In terms of its R-value, you can increase its efficiency by doubling or tripling the layers used. Batts come on a variety of thicknesses, which you can see in the table below:

Fiberglass insulation being installed in the underside of a home attic ceiling, showing a beige fiberglass batt
What a typical fiberglass batt looks like being installed.
Batt ThicknessR-value
3 ½ inch (8.89 cm)11
6 to 6 ¼ inches (15.24-15.88 cm)19
8 to 8 ½ inches (20.32-21.59 cm) 25
12 inches (30.48 cm) 38

The most commonly used batt-style insulation offers R-values between 2.2 to 3.8 per inch.

Loose-Fill Fiberglass Insulation

Loose-fill fiberglass insulation is made up of small particles of fiber that have not been worked into the same blanket form as mentioned above.

This type of insulation is better suited to unusual spaces or renovations, where the walls may be oddly shaped or too expensive to pull down.

Unfortunately, it requires a professional installing to come and prep the space and blow the insulation into the cavity. This is not a DIY option.

Since this type of insulation is not fixed at a certain thickness, you need to determine the R-value from the manufacturer or professional that comes to install it. 

However, in many cases, it is believed to have an R-value of about 2.2 to 2.7 per cubic inch. Therefore, to achieve the top R-value of 38, you would need 14-17 inches (35.56-43.18 cm) of loose-fill insulation. 

Fiberglass vs. Spray Foam

Since the two different types of fiberglass insulation are so similar, we’ll focus on the most user-friendly one for DIYers.

So, for the rest of this article, we’ll discuss how spray foam insulation compares to batt-style fiberglass insulation.

Here is a table comparing spray foam and fiberglass insulation and the better choice based on each criterion:

CriteriaSpray FoamFiberglassVerdict
R-value3.8 to 7 per inch (2.54 cm) 2.2 to 3.8 per inch (2.54 cm) Spray foam is more effective than fiberglass in insulation
Resistance to Moisture  WatertightCracks under moistureSpray foam is better for humid climates
DurabilityOver 50 yearsOver 50 yearsBoth are equally durable
Ease of installationHard: Involves mixing chemicals. Requires professional helpEasy: DIYers can do itFiberglass is better for those on a budget
CostMore expensiveCheaperFiberglass is better for those on a budget
Health risksGenerally safe to use if installed correctly. Poor installation increases risks such as skin, eye, and lung irritationGenerally safe to use if installed correctly. Incorrect installation causes the risk of inhaling tiny glass that can irritate the lungsBoth come with health risks that can be mitigated through proper installation

Let’s discuss each of the above aspects in more detail:

R-Value

R-value is one of the major deciding factors when picking an insulator.

R-value shows how well a substance resists heat flow. A high R-value means more heat will need to pass through the material before getting into your house.

According to The Department of Energy, the R-value for fiberglass ranges between 11 and 38—11 for 3.5-inches (8.89 cm) thick and 38 for 12-inches (30.48 cm) thick fiberglass.

On the other hand, the R-value for spray foam varies from 3.8 per inch (open-cell type) to 7 per inch (17.78 cm) (closed-cell type). 

This means that for a 3.5-inches (8.89 cm) thick insulation material, you get R-values of 13.30 and 24.5 using either open-cell or closed-cell spray foam, respectively. 

In contrast, both foam types offer R-values of 42 and 84 when you buy them in 7-inch sizes (17.78 cm).

In other words, spray foam offers higher resistance to heat flow, making it the better choice using this criterion.

Resistance to Moisture

The material used for insulation is also crucial because it must hold up well against moisture. Walls exposed to the elements, such as ones in basements and garages, are especially susceptible to moisture problems.

Notably, fiberglass tends to crack under moisture stress. It cannot dry out completely. 

Spray foam, on the other hand, has better resistance to moisture damage than fiberglass insulation. Because of that, spray foam is more effective in humid climates, so if you live in such places, it will help to pick spray foam.

Durability  

Both spray foam and fiberglass insulation can keep your home comfortable for over five decades.

But they age differently.

Fiberglass sags or settles with time, while the foam tends to shrink with age. That said, if installed correctly, both insulation types will last at least another 30 years before needing replacement again.

Ease of Installation

Installing fiberglass can be done by any DIY enthusiast. You buy the batts and rolls at a store, unroll them into your attic or floor joists, cut to fit around obstructions like chimneys and ducts on-site with scissors.

Spray foam insulation is more complicated than fiberglass because you need to mix hazardous chemicals before spraying it.

Therefore, it’s best to hire a professional who knows what they’re doing if you choose to go with this insulation.

Cost

Fiberglass insulation is cheaper than spray foam.  

On the other hand, spray foam costs a lot because you need to buy special equipment for mixing and spraying it. Besides, spray foam requires a professional installer to do the job.

However, remember that you get what you pay for. Spray foam has a better R-value per inch than fiberglass insulation gives.

Besides, spray foam is less likely to harbor moisture. It is also more resistant to damage from thermal stress due to changes in temperatures.      

Health Effects

Both fiberglass insulation and spray foam are generally safe to use if installed correctly.

However, fiberglass is made of glass fibers that can penetrate the lungs, lymph nodes, and other vital organs.

On the other hand, spray form contains isocyanates and other chemicals that have been linked to intestinal pneumonia, asthma, rhinitis, and bronchitis. 

Caution: Never attempt to install spray foam insulation on your own unless you are a certified professional and know how to mix the chemicals and the relevant precautions to take.

Here’s a YouTube video that summarizes the information above in 6 minutes (it also provides information on cellulose insulation in case you’re considering it as well):

The Pros and Cons of Fiberglass Insulation

Depending on the project, you may decide that spray foam insulation is too expensive, or you may even have trouble finding a company that has the time to come out to your build. 

Fiberglass is a great choice, but it does come with pros and cons. Below, I’ll cover a few of the key things to keep in mind before you choose this type of insulation.

Pros

Easy To Install

Fiberglass insulation can be rolled out on-site just like any other kind of insulation, and they typically come in standard sizes that fit joists and studs.

Fiberglass rolls also have paper facings that make them easier to cut with ordinary scissors. This means that DIY enthusiasts familiar with using tools could put up this type of insulation by themselves.

Inexpensive

Fiberglass insulation is cheaper than most other kinds of insulation. 

Notably, this material costs around $0.40 – $0.50 per square foot of area covered. In contrast, the cost of spray foam insulation is relatively higher, ranging between $1.00 and $1.50 per board foot.

Decent Soundproofing

Though fiberglass insulation doesn’t block sound as much as acoustic ceiling tiles or other types of regular insulation materials, it is still helpful in reducing noise from outside your home.

Tip: You could put fiberglass insulation on walls near your children’s bedrooms to avoid disrupting their sleep during noisy construction projects.

Eco-Friendly

Fiberglass insulation is made of recycled glass bottles that would otherwise be taken to your local landfill. It’s 100% recyclable, and, unlike polyurethane insulations, it won’t off-gas into the atmosphere even during decomposition.

Cons

Harmful if You Breathe It

Fiberglass batting gives off glass dust that is harmful when inhaled. If fiberglass insulation is improperly installed, the dust could get into your home’s air and affect your health as well as that of your family.

Fiberglass also tends to retain moisture; when this happens, mold growth is possible and might make you sick if you inhale it. So when installing fiberglass insulation in a wet area—like under the kitchen sink or bathroom shower stall—be sure to use a sealant or spray foam insulation instead.

Needs Protective Gear

Since fiberglass insulation is made of glass fibers, it can be dangerous to your health if you are not working with protective gear.  

You’ll need a disposable dust mask and gloves when installing fiberglass insulation or cutting the material open to fit spaces in walls.

Requires Vapor Barrier

Fiberglass insulation is not a vapor barrier by itself. When used with an improperly prepped construction site—one that has no plastic sheathing to protect the walls from liquid damage — water could leak through your walls.  

Therefore, fiberglass insulation needs a vapor barrier to keep any moisture away from your home’s framing and finishing.

If you need a sealant to waterproof fiberglass insulation, I recommend this Henkel Corporation Silicone Waterproof Sealant from Amazon.com.

It bonds well with fiberglass, wood, porcelain, stainless steel, and cultured marble, so you get a versatile product you can apply on different materials. Besides, the sealant is resistant to cracking, peeling, or sagging, making it a worthwhile option if you’re looking for a durable product.

Sagging Problem

Fiberglass insulation is bulky and heavy, so it can sag into your walls as you install it. The same can happen to the cardboard backing if not correctly applied or installed.

This brings about several problems, such as:

  • Uneven thermal insulation, resulting in either hot or cold spots within your home.
  • Mold growth that might make you sick.

Allergy Problems

Fiberglass batting is well-known for causing irritable skin reactions like rashes and allergies among people who live with it. Besides, it can aggravate bronchitis and asthma.

Health Tip: Before deciding on using any insulation, all members of your household should get a test done to check for allergies.  

Pros and Cons of Spray Foam Insulation

From the table above, you’ll see that spray foam is the most effective form of insulation, though it’s not the most wallet-friendly. 

Let’s go over some of the other pros and cons so you can make the most informed decision.

A man in full protective gear is sitting on the attic floor while he sprays spray foam insulation on the underside of the attic ceiling.
Spray foam is often more costly and messy, but provides better insulating value and a tighter seal.

Pros

Efficient

Spray foam insulation is a great way to prevent thermal bridging and improve the efficiency of your home.  

Because you spray it into place, it fills all those tough-to-reach spaces that are difficult to reach, such as around pipes and wires.  

Air and Watertight

Because it’s sprayed-in, spray foam creates an airtight barrier between your home and the climate outside so that you can save on heating or cooling costs.  

Another primary reason for using spray foam instead of fiberglass insulation is that it doesn’t require a vapor barrier. Instead, spray foam can double as a vapor retarder.

This means that you don’t need to protect your framing and finishings with plastic sheathing during construction, making installation easier and saving on materials costs.  

Cons

High Upfront Cost

One downside to spray foam insulation is its high upfront cost; it’s not cheap because the material is expensive. As I mentioned, it costs between $1.00 and $1.50 per board foot, almost triple the fiberglass insulation cost.

Besides, you should factor in labor cost since this method requires a professional to mix the chemicals.

Health Risks

As I mentioned, spray foam insulation comes with several health risks due to isocyanates, a class of chemicals used to make insulation foam.

These chemicals can affect the respiratory system negatively if you inhale them. Therefore, it’s essential to wear a protective breathing mask and ensure proper ventilation while installing spray foam for insulation purposes.

So, when do you choose either insulation?

Here is a chart that would come in handy when making this decision:

Is Insulation Toxic and Dangerous? (What You Should Know)

Most insulation is toxic and dangerous with some of its health risks including breathing difficulties, cancer, and skin, eye, and lung irritation. However, most of these risks can be managed by ensuring you wear appropriate safety gear, and that the insulation is installed correctly. 

Here are common insulation types and their associated health risks:

  • Fiberglass: Skin and eye irritation, Stomach discomfort, Sore nose or throat.
  • Asbestos (Banned due to its toxicity): Lung cancer.
  • Cellulose: Irritates mucous membrane, eyes, nose, and throat causes diarrhea (mostly harmful when it burns).
  • Spray Form: Irritates skin, eyes, and lungs.
  • Rigid form with flame retardants: Headache, nausea, and vomiting.

Caution: Do not use asbestos for insulation. It is illegal and poses severe long-term health risks if inhaled.

Final Thoughts

Despite their cons and associated health risks, fiberglass and spray foam insulation come in handy when you need to keep power consumption in your home minimum. If installed properly, they can serve you for over five decades.

That said, homeowners who want to decrease their environmental footprint and live a greener lifestyle should consider fiberglass insulation. It is made from renewable resources that can be recycled or reused when the product reaches its end of life. However, those keener on thermal resistance or stay in humid areas should pick spray foam insulation.

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