Fiberglass insulation is significantly cheaper than spray foam insulation but it is also less effective, especially in extremely cold conditions. Fiberglass insulation is the most common form of home insulation (used in roughly 85% of American homes), while spray foam insulation has less market share but is increasing in popularity. Professional installation is required for spray foam insulation but fiberglass insulation can often be installed by homeowners themselves.
edit How it works
Fiberglass insulation contains billions of tiny glass fibers, which contain trapped bubbles of air. These air bubbles slow the transfer of heat.
Spray foam contains a polymer, such as polyurethane, and a foaming agent. After being sprayed, it expands to roughly 100 times its original volume and hardens into a solid. As a result, it is able to fill vacant air gaps, and will expand and contract in relation to the building.
edit Types of Spray Foam insulation
There are 2 types of spray foam insulation — Closed Cell (CC) and Open Cell (OC). With the open-cell vs. closed-cell issue, there are two major factors to understand and consider.
The first is the nature of the foam. It is either open-cell foam, where the tiny cells of the foam are not completely closed. They are broken and air fills all of the “open” space inside the material. This makes the foam weaker or softer feeling than closed-cell foam. Closed-Cell foam differs in that all of its tiny foam cells are closed and packed together. They are filled with a gas that helps the foam rise and expand and become a greater insulator. These cells can be formulated to obtain many characteristics, the most common being size and density.
Density is measured by weighing one solid cubic foot of foam material. Open Cell foams typically weigh in at 0.4 to 0.5lb./cu. ft. Closed cell foam for insulation applications range in density from 1.7 lb./cu. ft. to 2.0 lb./cu. ft. Roofing applications typically use a 2.8 to 3.0+ lb./cu. ft. to support traffic and loads better. The higher the density the foam, the heavier, or stronger it becomes. Some polyurethane foams are molded into decorative interior molding and painted or stained for a simulated wood effect. These “higher density” foams are typically in the 30 lb./cu. ft. to 40 lb./cu. ft. density range.
The advantages of closed-cell foam compared to open-cell foam include its strength, higher R-value, and its greater resistance to the leakage of air or water vapor. The disadvantage of the closed-cell foam is that it is denser, requires more material, and therefore, is more expensive. Even though it has a better R-value, typically the cost per R is still higher than open-cell foam.
The choice of foam can also be based on the requirements for the other performance or application-specific characteristics such as strength, vapor control, available space, etc. Open-cell SPF has an R-value around 3.5 per inch and typically uses water as the blowing agent. Closed-cell SPF has an R-value of around 6.0 per inch (aged R-value) and uses high R-value blowing agents.
edit Energy efficiency of spray foam vs fiberglass
Fiberglass insulation cannot stop air from passing through it, meaning that more than 30% of heat or air conditioning can escape. Poorly installed fiberglass can also leave spaces around fixtures, allowing for more heat or cool air to escape.
Spray foam insulation fills all spaces, preventing air from escaping. It acts as an air barrier. Spray foam insulation also has a higher R-value. So it is significantly more efficient than fiberglass insulation.
edit 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 you need insulation that is about 6.3 inches thick to reach R-38. The R-value of fiberglass insulation is approximately 2.2 per inch so you need much thicker fiberglass insulation to achieve the same R-value of 38.
edit Installation Process
edit How spray foam insulation is installed
Spray foam insulation is composed 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 need to be properly agitated before use so that the fire retardant mixes well with the entire resin. Each barrel is slowly warmed to about 770 °F before beginning application. Transfer pumps draw the product out of each 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 actually contains 3 hoses) runs from the proportioner to the spray foam gun. There is a mixing chamber in the gun head whre the isocyanate and resin mix and are immediately sprayed and applied.
Spray foam insulation must always be installed by a professional. This is a great overview of the installation process for spray foam insulation and the following video demonstrates how professionals install spray foam insulation in the attic of a home:
edit How fiberglass insulation is installed
Fiberglass insulation usually comes in batts or rolls. In order to be completely effective, fiberglass insulation must be cut carefully around obstacles such as power sockets. This can be incredibly time consuming. If an individual is willing to settle a less effective job, fiberglass can be easily installed without professional assistance.
Fiberglass can irritate your throat and skin, so wear protective gear. Buy a two-strap mask rated for fiberglass insulation (3M No. 8210 is one example) and wear a hat, gloves, a long-sleeve shirt and goggles to keep fibers out of your eyes.
Here's an informative video about overcoming 3 main problems in installing fiberglass insulation:
edit Cost of fiberglass vs spray foam insulation
On the whole, spray foam insulation costs two to three times as much as fiberglass insulation. Fiberglass insulation costs around $0.40 per square foot. Spray foam can be significantly more expensive, but can lead to bigger savings on heating and cooling costs. It costs around $3 per square foot, with a thickness of 3 inches.
Given the complexity of the installation process for spray foam insulation, the cost to install it are also significantly higher than fiberglass.
Spray foam, however, lasts a lifetime and can be applied in nooks and crannies that are not suitable for fiberglass. With its higher energy efficiency 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.
edit Health Effects and Risks
Spray foam insulation contains isocyanates, which are powerful irritants to the eyes, gastrointestinal tract and respiratory tract. Direct skin contact with isocyanates can also cause inflammation and rashes on arms, chest, and neck. Overexposure to isocyanates can also sensitize workers, making them susceptible to asthma attacks if they are exposed again. Respiratory irritation may progress to a chemical bronchitis. Spray foam insulation is typically non-toxic only after it has cured. While curing, spray foam emits a gas that causes blurred vision and trouble breathing. If the material is not mixed in the right proportions, it can emit toxic gas perpetually.
Fiberglass insulation contains glass wool fibers that are believed to be carcinogenic. Some fiberglass products warn of "possible cancer hazard by inhalation". Fiberglass irritates the eyes, skin and respiratory system. Potential symptoms include irritation of eyes, skin, nose, throat; dyspnea (breathing difficulty); sore throat, hoarseness, and cough.
Protective gear is recommended when installing either type of insulation.