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Fiberglass insulation is significantly cheaper when compared to spray foam insulation, but it is also less effective, especially in extremely cold conditions.
Used in roughly 85% of American households, fiberglass insulation is the most common form of home insulation. Spray foam insulation has less share in the market but is increasing in popularity.
Professional installation is needed for spray foam insulation, but property holders themselves can often install fiberglass insulation.
Contents: Fiberglass Insulation vs. Spray Foam Insulation
How It Works
The process of transferring heat is slowed down with fiberglass insulation because the glass fibers trap air bubbles. These bubbles create an insulating impact by slowing heat exchange between areas and surfaces.
Spray foam contains a polymer, like polyurethane, and a foaming agent. After being sprayed, it expands to roughly 100 times its original volume and hardens to form a solid. As a result, it can fill vacant air gaps and will expand and contract concerning the building.
Energy Efficiency of Spray Foam vs. Fiberglass
The composition of fiberglass insulation doesn’t stop air from passing through it. On average, over 30% of heat or air conditioning escapes where fiberglass insulation is installed. If poorly installed, fiberglass can leave spaces around fixtures, allowing even more heating or cooling to escape.
Spray foam insulation fills all spaces, stopping air from escaping. It acts as an air barrier. Like cellulose insulation, spray foam insulation is significantly more effective than fiberglass and has a higher R-value.
R-Value
A product’s R-value is its resistance to heat flow. A higher R-value prevents more heat from escaping through the insulation. Homes generally try and reach an R-value of 38 with their insulation. The R-value of spray foam insulation is approximately 6 per inch, so those using spray foam as their insulator will need about 6.3 inches of thickness to reach R-38. The R-value of fiberglass insulation is approximately 2.2 per inch, so much thicker fiberglass insulation is required to achieve the same R-value of 38.
Installation Process
How Spray Foam Insulation Is Installed
Spray foam insulation comprises of two separate parts that are combined as they are sprayed. One barrel is isocyanate (the “A” side), and the other barrel is resin (the “B” side). One of the components in the “B” side barrel is the fire retardant. The components in this barrel must be correctly agitated before use so that the fire-retardant mixes well with the entire resin. Every barrel is slowly warmed to about 770 °F before beginning application. Transfer pumps draw the product out of every barrel and move it to the proportioner, which controls the amount of product drawn from each barrel and heats the products to the appropriate spray temperature (usually around 150-1600F). A hose (that contains 3 hoses) runs from the proportioner towards the spray foam gun. There is a mixing chamber in the gun head where the isocyanate and resin mix and are instantly sprayed and applied.
How Fiberglass Insulation Is Installed

Installing Spray Foam Insulation
Fiberglass insulation comes in batts or rolls of varying thicknesses and lengths that require to be cut for installation. For the highest insulation level, the fiberglass must be cut carefully to fit as tightly as possible around obstacles such as power sockets. This procedure is complicated for some installations and is time-consuming. For quick insulation, fiberglass can be easily installed without professional help, the most benefits will accrue if a professional does the job.
Fiberglass can irritate your throat and skin, so you need to wear protective gear. Buy a two-strap mask rated for fiberglass insulation (3M No. 8210 is one instance) and wear a hat, gloves, a long-sleeve shirt, and goggles to keep fibers out of your eyes.
Cost of Fiberglass vs. Spray Foam Insulation
On the whole, spray foam insulation costs two to three times more than fiberglass insulation. Fiberglass insulation costs about $0.40 per square foot. Spray foam can be significantly more expensive but can result in more significant savings on heating and cooling costs. It costs around $3 per square foot, with a thickness of 3 inches.
Due to the complexity of the installation process for spray foam insulation, the cost to install it is also significantly higher than fiberglass.
Spray foam, however, lasts a lifetime and can be applied in nooks and crannies that are not fit for fiberglass. With its higher energy effectiveness and lower utility bills, the payback period for offsetting the higher cost of spray foam insulation is estimated at between 5 and 7 years for colder climates.