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.
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 get blown into the wall cavity once covered with a protective layer of mesh fabric.
Let’s take a look at these in more detail below.
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 in a variety of thicknesses, which you can see in the table below:
|3 ½ inch (8.89 cm)
|6 to 6 ¼ inches (15.24-15.88 cm)
|8 to 8 ½ inches (20.32-21.59 cm)
|12 inches (30.48 cm)
The most commonly used batt-style insulation offers R-values between 2.2 and 3.8 per inch.
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 installer 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 who 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.
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:
|3.8 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
|Cracks under moisture
|Spray foam is better for humid climates
|Over 50 years
|Over 50 years
|Both are equally durable
|Ease of installation
|Hard: Involves mixing chemicals. Requires professional help
|Easy: DIYers can do it
|Fiberglass is better for those on a budget
|Fiberglass is better for those on a budget
|Generally safe to use if installed correctly. Poor installation increases risks such as skin, eye, and lung irritation
|Generally safe to use if installed correctly. Incorrect installation causes the risk of inhaling tiny glass that can irritate the lungs
|Both come with health risks that can be mitigated through proper installation
Let’s discuss each of the above aspects in more detail:
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-inch (8.89 cm) thick insulation material, you get R-values of 13.30 and 24.5 using either open cell or closed cell 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.
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.
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.
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, and cut them 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.
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.
Both fiberglass insulation and spray foam are generally safe 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 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):
Energy Efficiency of Fiberglass vs. Spray Foam
Energy efficiency is a crucial consideration when choosing the right insulation material for your home. So, between spray foam and fiberglass, which one is the best in terms of energy efficiency?
The energy efficiency of fiberglass is not without its limitations. Fiberglass insulation composition does not inherently stop air from passing through it. As a result, it allows a significant amount of heat or air conditioning to escape when installed in buildings.
On average, over 30% of heating or cooling can escape through areas with fiberglass insulation, leading to energy loss and higher utility bills.
One of the common issues with fiberglass insulation is poor installation, which can further exacerbate its energy efficiency problems.
Inadequate installation can lead to gaps and spaces around fixtures, creating pathways for heated or cooled air to escape. This significantly reduces the insulation’s effectiveness.
Spray Foam Insulation
In contrast, spray foam insulation is a high-performance insulation option that excels in terms of energy efficiency. It acts as a superior air barrier, effectively sealing all spaces and preventing the unwanted exchange of indoor and outdoor air. Consequently, spray foam insulation is a standout choice when it comes to energy efficiency.
The energy efficiency of spray foam insulation is comparable to that of cellulose insulation, which is known for its effectiveness in retaining indoor temperatures.
Spray foam insulation, like cellulose, boasts a higher R-value. A higher R-value signifies better insulation performance and enhanced energy efficiency.
Spray Foam Vs. Fiberglass Insulation: Installation Process
As mentioned, spray foam and fiberglass insulations are installed differently. In this section, I’ll give you a glimpse into how each is installed.
Spray Foam Insulation Installation
Installing spray foam insulation incorporates two components—isocyanate (side “A”) and resin (side “B”).
The resin includes a fire retardant that makes this insulation more fire-resistant. It’s worth noting that spray foam insulation is not fire-resistant. Therefore, the fire retardant in the resin lowers the possibility of the insulation igniting and burning when exposed to a heat source.
Before the installation, the isocyanate and resin are heated to approximately 770°F (410℃). Heating is necessary to attain the optimal temperature under which the chemicals can react to create a foam.
After heating, transfer pumps are used to draw the materials from their respective barrels to the proportioner. The proportioner regulates the quantity and temperature, which should be between 150 and 160°F (65.56 and 71.11℃).
Finally, a specialized hose with three channels is used to connect the proportioner to the spray foam gun. The mixing chamber within the gun combines the isocyanate and resin, which are then immediately sprayed and applied.
The application process makes spray foam ideal for unvented attic insulation.
Expert Advice: Spray foam insulation must be installed by a trained professional because the intricacies of the process require expertise.
Fiberglass Insulation Installation
Fiberglass insulation comes in batts and rolls of varying dimensions. Therefore, these insulation materials must undergo customization before installation.
The customization involves measuring and cutting the insulation based on the size of the area to be insulated. It’s recommended to add an extra inch before cutting for a tight fit. A utility knife with a snap-off blade is ideal for cutting through thick batts.
The installation process begins once the insulation is cut to the desired dimensions. Ideally, the insulation is pressed between two wall studs, with the moisture barrier facing outwards. The pressing is gentle (no compression) to trap air within the insulation for the best results.
Finally, staples are used to fasten the tabs to the stud edges.
It’s worth mentioning that fiberglass can irritate the skin and throat. Therefore, it’s crucial to wear protective gear like a two-strap mask, a hat, gloves, a long-sleeve shirt, and goggles.
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.
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.
Fiberglass insulation is cheaper than most other kinds of insulation.
Notably, this material costs around $0.40 – $0.50 per square foot area covered. In contrast, the cost of spray foam insulation is relatively higher, ranging between $1.00 and $1.50 per board foot.
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.
Fiberglass insulation is made of recycled materials, mostly 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.
Fiberglass batt insulation 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—use a sealant or spray foam insulation instead.
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.
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 for waterproof fiberglass insulation, I recommend this Henkel Corporation Silicone Waterproof Sealant.
It bonds well with fiberglass, wood, porcelain, stainless steel, and cultured marble, so you get a versatile product you can apply to 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.
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:
- Mold growth that might make you sick.
- Uneven thermal insulation resulting in either hot or cold spots within your home.
Fiberglass batts are well-known for causing irritable skin reactions like rashes and allergies among people who live with them. Besides, they 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.
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.
Spray foam is often more costly and messy, but provides better insulating value and a tighter air sealing capability.
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.
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 home insulation is that it doesn’t require an air barrier. Instead, spray foam can double as a vapor retarder.
This means you don’t need to protect your framing and finishings with plastic sheathing during construction, making installation easier and saving on materials costs.
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 costs since this method requires a professional to mix the chemicals.
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 home insulation purposes.
So, when do you choose either insulation?
Here is a chart that would come in handy when making this decision:
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. These risks include colon cancer, lung cancer, and mesothelioma.
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 to a 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 keen on thermal resistance or staying in humid areas should pick spray foam insulation.
- Energy.gov: Types of Insulation
- Illinois Department of Public Health: Fiberglass
- Illinois Department of Public Health: Environmental Health Fact Sheet: Fiberglass
- The United States Environmental Protection Agency: Chemicals and Production of Spray Polyurethane Foam – Why It Matters
- Oak Ridge National Library: Thermal Performance of Fiberglass and Cellulose Attic Insulations
- Oak Ridge National Library: Closed Cell Foam Insulation: A Review of Long Term Thermal Performance Research
- Green Built: Airtightness and Spray Foam Insulation
- Energy.gov: Types of Insulation