Fiberglass Vs. Spray Foam Insulation: Read This Before Buying!

Fiberglass and spray foam have clear differences, but both are very effective insulation materials. Fiberglass batt is more commonly used of the two, probably because it is the cheaper option.

Fiberglass refers to a series of very delicate fibers that are made of a number of recycled materials, but mainly glass. The glass fibers are held in one unit using adhesive backing which usually serves as a vapor barrier.

There are two common packages of fiberglass commonly known as batts and loose-fill. Batts are in the form of large blankets and usually bear striking resemblance to cotton candy.

On the other hand, spray foam insulation refers to a liquid chemical that expands to form airtight seals when forced out of a spray can and is used to seal voids and any forms of cracks that air can flow through.

Like fiberglass, spray foam comes in two varieties – open cell and closed cell. Open cell foam refers to the flexible and soft foam. They are not fully enveloped like the closed cell foam type. Because the closed cell type has cells that are completely pressed down against each other, they are more rigid, dense and more stable.

Fiberglass is relatively cheaper than spray foam. Although not very effective in extreme cold conditions, fiberglass insulation is more common with about 85% of Americans using it. The use of spray foam is rising however. It is also important to note that installation of spray foam requires some expert skills while fiberglass can be installed by any homeowner with relative ease.


Fiberglass Insulation

Spray Foam Insulation

Cost About 0.4 USD per square foot Between 0.90 – 1.50 USD per board
Installation Sheets placed in the wall Foam sprayed by professional/expert
Resistance to Moisture Yes Yes
Air leakage Yes No leakage in closed cell type.Minimal leakage in open cell type
Energy Efficiency Less efficient More efficient
Extreme Cold Loses heat quickly Does not impact performance
Flammability Potentially as a result of presence of kraft paper in batts Yes – barrier with fire such as drywall required. Most closed cell types come with firewall retardants.
Lifetime 10-25 years if kept dry Over 80 years
R-Value 2.2 per inch non aged R-value.Material loses R-value with time Open cell has 3.5 per inch of aged R-value.Closed cell has 6 – 7 per inch of aged R-value.

Material does not lose R-value over time.

Benefits Lower cost installation Material stops moisture and air infiltrationIt adds more strength to the structure of the building

It is permanent and does not sag

Eliminates pollen and dust

Reduces wear and maintenance requirements of HVAC equipment

Added Structural Integrity None Closed cell adds up to 250% Racking strength to the roof and wall
Sound Barrier Efficiency Low to moderate High

How It Works

With fiberglass insulation, heat transfer is slowed down by the glass fibers which trap air bubbles. The bubbles in turn slow down heat exchange between the surface and other areas and cause an insulating effect.

On the other hand, spray foam is made up of a foam agent and polymers. Once it is sprayed, the foam expands by over 100 times the original volume before hardening into a solid. This way, it fills air space and gaps.

Energy Efficiency of Fiberglass Vs. Spray Foam

Fiberglass insulation is inefficient in stopping air or heat from passing through it. In fact, it takes an additional work to be able to create airtight seals with fiberglass. About 30% of air or heat is known to escape from buildings where fiberglass is installed.

In fact, if this insulation is not correctly installed, it can easily leave space between fixtures and allow even more cooling or even heating to escape the building. This makes it less efficient in heat or air conditioning. This is one reason why a DIY approach to the installation of fiberglass may not be a good idea.

In addition, installing high-density fiberglass may be required in order to improve the energy efficiency in a limited space. If correctly done by a professional, the material does excellent work in keeping homes warm in winter and cool in summer.

On the contrary, spray foam fills all the available spaces. It creates both an insulation barrier and air barrier at the same time. This way, it prevents heat or air from escaping the building, reduces the chances of mold occurring and increases home energy efficiency.

Like cellulose, spray foam provides an air barrier which makes it more efficient in insulation than fiberglass. The material therefore offers more energy efficiency compared to fiberglass and this can be directly attributed to its air sealing combo and high R-value.


The R-value of a product is precisely the resistance it offers against heat flow. Higher R-values retain more heat and therefore are better able to stop heat loss from a building. Many homes try to achieve R-values of 38 or higher.

Spray foam provides the highest R-Value for every inch that is installed when compared to the other insulation materials. This is because the material completely seals up and provides complete insulation to the “building envelope”. This ensures more efficient thermal insulation to every building where the foam is used.

Spray foam can either be open cell or closed cell. Usually, open-cell is R-3.5 to R3.6 while closed foam has approximately 6 per inch of R-value. This means that those who decide to use the material in their insulation have to use up to 6.3 inches of spray foam thickness to be able to get R-38.

Both loose-fill fiberglass and fiberglass batts offer reasonable R—values particularly if they are professionally installed. However, considerable loses of thermal protection may occur as the product settles over its lifetime. That’s especially true of loose-fill fiberglass and if the material is not installed by an expert. This scenario will usually require “topping up” in the long term to improve heat insulation efficiency of the material. It can be mitigated by ensuring the whole installation process is done well, without leaving any serious gaps.

Fiberglass insulation has a very low R-value – 2.2 per inch. If you choose to use fiberglass for your insulation needs, you’ll need a thicker material than you’d need with spray foam to be able to achieve the recommended R-38 value. The table below shows a number of R-values and their zones of application (

Vapor/Moisture Barrier

Spray foam acts perfectly as a vapor barrier once correctly installed. However, this highly depends on the type of foam being used. In order to be able to make the right decision on what type of foam to use, a professional is needed. This will help through deciding the best approach as well as legal requirements for installation.

Fiberglass on the other hand is not able to develop a vapor barrier by itself. This means that a separate vapor barrier is needed for every installation of the material. A professional technician should therefore be engaged throughout the process since a DIY or an inexperienced installer may not well understand every detail about proper installation of the product.

Insulation Processes

Installation Of Fiberglass

Fiberglass generally comes in standard sizes of batts.  This makes installation easier especially in wall studs or ceiling joists. In irregular-sized parts of a building, the batts are usually custom-cut to the right sizes before they can be installed. Additionally, in order to achieve greater insulation effect, the material must be cut to the right size in order to fit tightly around particular obstacles such as the power sockets. The process therefore consumes more time and is equally difficult depending on the structure of the building where the installation is meant to be.

Although quick fiberglass installation can be achieved without expert assistance, you are more likely to get greater insulation when it is done by a professional. Maximum performance can be achieved by air sealing.

In addition, fiberglass may be very irritating to both skin and throat especially if not properly handled. It is therefore advisable that appropriate protective gear is used in the process. Some of the very important gear one needs to safely install fiberglass include a hat, long-sleeve shirt, gloves, goggles and a two-strap mask specifically rated for insulation of fiberglass (e.g. 3M No. 8210).

Installation Of Spray Foam Insulation

This is much more complex than fiberglass batts insulation. Both professional handling and specialized equipment are required for the installation process. Spray foam is a highly priced product but achieves complete air sealing during installation without requiring any extra steps.

During this process, two separate parts of the material contained in two separate barrels are combined – the “A” side also called isocyanate and the “B” side also called resin. The “B” side is made up of other components such as fire retardant and should be adequately agitated before they can be used in order that the fire retardant properly mixes with resin.

Before application is started, ensure the barrels are heated to about 770 0F. Once this is done, transfer pumps are used to draw out and transfer the product from each barrel to the proportioner. The proportioner controls the amount of each product that is drawn from each of the two barrels, heat it up to the right temperature (150 – 160 0F).

A three-prong horse connects the spray foam gun to the proportioner. The gun head has a mixing chamber where resin and isocyanate mixing occur and are sprayed and applied immediately after. This process is usually administered by a professional.

Cost Of Spray Foam And Fiberglass Insulation

Spray foam is much more expensive compared to fiberglass, up to two or three times more. While fiberglass costs around 0.4 dollars per square foot, spray foam costs around 3 dollars per square foot. But although spray foam is much more expensive, it is more economical in the long run.

In addition, spray foam insulation is suitable for crannies and nooks installation where fiberglass may not be efficient. However, the installation costs of spray foam are equally high and this adds up to the general costs. These costs are however easier offset with lowers energy bills. In colder climates, only 5 to 7 years are needed to offset the costs of spray foam.

Health Risks And Effects

The chemical composition of spray foam are highly irritating compounds that can result in allergic reactions when in contact with the eye, skin and lungs, resulting in severe rashes or inflammation.

As a result, proper protective gear such as gloves, respirators, goggles and clothing must be worn during installation of spray foam. Research shows that excessive exposure to isocyanates has a potential to cause asthma and inexperienced workers who install spray foam are much more exposed. Other long-term effects of exposure are bronchitis and other fatal ailments.

Spray foam also emits a gas that has the potential to cause blurred vision and even respiratory distress in the process of curing. In addition, the foam has chances of continuing to emit the dangerous gas for longer periods of time especially if the foam components are not efficiently mixed. If components are properly mixed and once cured however, it is inert and remains permanently non-toxic.

On the other hand, fiberglass components are believed to contain carcinogenic glass wool fibers and are high alert for possible cancer hazard especially by inhalation. Fiberglass also irritates skin, eyes and the respiratory system. When affected, common symptoms include hoarseness, cough, irritation of throat, nose, skin, eyes and even difficulty in breathing also known as dyspnea.

Thermal Barrier

Thermal barrier protection is an essential element in home insulation and both spray foam and fiberglass must be guarded. Any exposed insulation part of spray foam should therefore be secured with a special coat of thermal barrier. This will provide adequate safety against fire and equally safeguard the material itself.

Fiberglass on the other hand has a natural fire retardant but depends on the type under use. Some are fire retardant, and others aren’t, so pay attention to this feature of the product before buying.

Cost Effectiveness

Stand alone value is one of the key factors one considers in choosing a good insulation apart from the R-value. By factoring in cost, fiberglass offers a better payoff, immediately. While you pay more for a higher thermal performance in spray foam, fiberglass has the ability to provide a closer efficiency when professionally installed at a lower cost.

The two materials are both good at trapping air and can save a lot of money that would otherwise be covering energy bills. Fiberglass however conserves almost 12 times the amount of energy it generates and can cut your utility bills by almost 40% every year.

Final Word

It is crystal clear from the description that spray foam is the best choice for home insulation especially for having the highest R-value. However, picking the best material to insulate your home is not as simple as selecting a material with a higher R-value. Factors that must be put together are:

  • Budget
  • Space
  • Potential safety risks
  • Climate

Hopefully this article has provided you with much needed information and made your choice easier. Hope this helps!

Similar Posts