Building Insulation Performance Comparison

Features Fiber Glass Cellulose Rock/Slag Wool Cotton Spray Foams Open Cell Spray Foams Closed Cell
Thermal Performance
R-value ranges - Batts
2 x 4 wall (3.5”)
2 x 6 wall (5.5”)
R-13 to R-15
R-19 to R-21
N/A
N/A
R-13 to R-15
R-22 to R-23
R-13
R-19 to R-21
N/A
N/A
N/A
N/A
Thermal Performance
R-value ranges - Blown-In
2 x 4 wall (3.5”)
2 x 6 wall (5.5”)
R-13 to R-15
R-20 to R-23
R-12 to R-13
R-19 to R-20
R-14.5
R-23
N/A
N/A
R-12 to R-13
R-19 to R-20
R-19 to R-22
R-32 to R-35
Settling Batts: No settling
Blown-In: Virtually no settling. Does not impact R value.
Batts: N/A
Blown-In: (Dry)
In attics, can settle up to 20% - losing R-value.
Batts: No settling.
Blown-In:
Virtually no settling.
Does not impact R-value.
Batts: No settling. Shrinkage may occur over time. Shrinkage may occur over time.
Fire Performance Naturally fire resistant. Naturally flammable. Cellulose insulation manufacturers must
apply 20 to 23 percent, by
weight, of fire retardants to reduce flammability.
Naturally fire resistant. Flammable. Must be treated with fire retardants. Can be consumed by flame. Exposed foam should be protected using a 15-minute thermal barrier required when installed in a habitable area. Can be consumed by flame. Exposed foam should be protected using a 15-minute thermal barrier required when installed in a habitable area.
Corrosiveness Non-corrosive. When chemical fire retardants are used, it can lead to corrosion. Non-corrosive. Fire retardant chemicals can cause corrosion. Non-corrosive. Non-corrosive.
Moisture Absorption
Building codes require vapor
retarders to be installed on the
“warm-in-winter” side of most
walls in cold climates.
Will not absorb and retain moisture. Will absorb moisture and “mat down,” losing R-value. Absorbed moisture can wash away the applied fire retardant. Will absorb moisture and hold it until drying conditions occur. Will not absorb and retain moisture. Can hold up to 15% moisture. Repeated wetting and drying
can cause borate treatment to leach out and mold to grow
Can absorb, but not retain moisture. Will not absorb and retain moisture. Closed cell foams of sufficient thickness do not need vapor retarders.
Drying Time Required
(Blown-In Applications)
No. Yes. No. No. A drying or curing time is
required.
A drying or curing time is
required.
Installation Considerations For blown-in, professional
installation is recommended.
The installer must use a machine capable of installing fiber glass.
Dry application: Do it yourself.
Wet application: Professionally installed using a blowing machine to add water. To prevent fires, heaters and recessed light fixtures must not
come in contact with product.
For blown-in, professional
installation is recommended. The installer must use a
machine capable of installing rock wool. Blows at high speeds.
Do it yourself.
Difficult to cut without a motorized cutting tool.
Requires professional installation. A fire extinguisher should be
close at hand during installation.
Requires professional installation. A fire extinguisher should be
close at hand during installation.
Recommended Work
Practices
For batt and blown-in installations, manufacturers have established recommended work practices. Industry lacks recommended work practices. NIOSH
recommends personal
protective equipment.
For batt and blown-in installations, manufacturers have established recommended work practices. Industry lacks recommended work practices available. Use of fire retardants would dictate use of personal protective equipment. Some manufacturers have recommended work practices. Significant risks dictate use of a full-face air respirator, coveralls
with hood, boot covers, gloves for the applicator and the helpers working in the vicinity.
Some manufacturers have recommended work practices. Significant risks dictate use of a full-face air respirator, coveralls
with hood, boot covers, gloves for the applicator and the helpers working in the vicinity.
Reuse Yes. No. Yes. Yes. No. No.
Major Raw Material Components Recycled glass and sand, a renewable and abundant resource. Newspapers or wood fiber treated with chemical fire retardant. Minerals like basalt or diabase and blast furnace slag. Recycled or raw cotton treated with chemical fire retardants. Water, HFAs, MDIs, diisocyanates, polyol compounds. HCFC and HFA gases, CFCs, MDIs, diisocyanates, polyol resins.
Product Testing for Health Safety Thoroughly tested product. Very limited health and safety testing. Thoroughly tested product. No known health and safety testing. No known health and safety testing. No known health and safety testing.
Recycled Content Yes. Yes. Yes. Yes. No. No.

*Reference: NAIMA - North American Insulation Manufacturers Association

 

Installed Cost of Insulation

A sustainable insulation product must also be cost effective. In fact, cost is as important a factor as the other performance attributes listed in the table above. Installed insulation costs vary and you will need to weigh those costs against the benefits. The key is to install the most cost-effective, high performing, sustainable insulation product to improve the energy and environmental performance of the home.  

Thermal Resistance R-Value

The thermal resistance of insulation is designated by R-value. R-value is resistance to heat flow - the higher the R-value, the greater the insulating power. Thickness of insulation is only one factor that determines its R-value. To ensure that consumers are provided with accurate information regarding R-values, the Federal Trade Commission (FTC) has established a rule which mandates that specific R-value information for home insulation products be disclosed in ads and at the point of sale. The purpose of the FTC R-value disclosure requirement for advertising is to prevent consumers from being misled by certain claims which have a bearing on insulating value. When insulating a home, it is important that the homeowner gets the R-value specified and that the thermal performance lasts over time. In comparing the insulating properties of fiber glass versus cellulose insulation, the important thing for consumers to compare is not the R-value per inch of the products but the R-value provided by the products for the space to be insulated.

Fiber Glass Insulation: The ability of fiber glass insulation to provide the desired R-value for a given space equals or exceeds the ability of cellulose insulation. Fiber glass insulation is offered in different densities, which allows you to achieve different R-values for a given space.

Cellulose Insulation: Cellulose insulation manufacturers promote their products as having “higher R-value per inch.” This is simply not true given the range of fiber glass products available. Moreover, the R-value Rule specifically states “do not give the R-value for one inch or the ‘R-value per inch’ of your product” because representing a product’s R-value per inch is “clearly leading consumers to believe that insulation R-values are linear.”  

Settling and Loss of R-value

Settling is important in insulation product selection because it directly relates to the installed thermal performance over time.

Fiber Glass Insulation: Properly installed fiber glass batts and rolls do not settle. Fiber glass loose-fill insulation will experience negligible settling (less than 2%) over time. When manufacturers’ installation procedures are employed, fiber glass insulation maintains its thermal performance for the life of the building.  

Cellulose Insulation: Cellulose manufacturers agree that their products settle over time. Most set the settling rate at about 20%. Therefore, always consult the “minimum settled thickness” and the “initial installed thickness” listed on the cellulose manufacturer’s coverage chart, which is required by the FTC, to ensure future settling is accounted for.   

 

Fire Safety

Fire resistance is an important attribute of any insulation material. It is in a homeowner’s best interest to consider the flame-resistance properties of the insulation in his or her home. In terms of fire safety, fiber glass and cellulose perform quite differently.  

Fiber Glass Insulation: Fiber glass insulation is made from sand and other inorganic materials which are melted and then spun into glass fibers. Fiber glass is naturally noncombustible and remains so for the life of the product. It requires no additional fire-retardant chemical treatments. Unfaced fiber glass insulation is recognized by building code groups as an acceptable fire stop in residential wood frame walls. Kraft and some foil facings available on fiber glass insulation are themselves combustible. Products with combustible facings should not be left exposed. When properly installed, in substantial contact with a code approved thermal barrier, these products do not pose a fire hazard.

Cellulose Insulation: Cellulose insulation is made of ground-up or shredded newspaper which is naturally combustible. In fact, cellulose insulation is regulated as a recognized fire hazard by the Consumer Product Safety Commission (CPSC). To protect against fire hazards, cellulose insulation is heavily treated with fireretardant chemicals prior to installation. These fire-retardant chemicals can leach out of the cellulose insulation over time. Tests conducted by the California Bureau of Home Furnishings and Thermal Insulation have demonstrated that some cellulose samples failed the standard fire safety test only six months after installation. Additionally, smoldering combustion and re-ignition problems are concerns with cellulose insulation should a fire start. Even properly treated cellulose insulations will burn at about 450°F, the surface temperature of a 75 watt light bulb. 

Resistance to Corrosion

Products that may cause corrosion problems in a home should be avoided.  

Fiber Glass Insulation: Fiber glass insulation is not corrosive and contains no chemicals that can corrode pipes and wires. Cellulose Insulation: Certain chemicals routinely applied as a fire retardant to most cellulose insulation (particularly the sulfates) can cause the corrosion of pipes, wires, and fasteners under some conditions.  

Moisture Absorption

In general, insulation will lose R–value when wet. However, there are important differences in the water vapor absorption properties of the two insulations which can impact their installed performance.  

Fiber Glass Insulation: Insulation made of fiber glass is not absorbent. Under normal conditions, all insulation is exposed to humidity in the air. Fiber glass will not wick up and hold water, thus it resists permanent loss of R-value. Because it is inorganic, it is naturally fire resistant. If fiber glass insulation becomes saturated as the result of flooding or other catastrophic events, the manufacturer of the product should be consulted to determine whether the product should be replaced.

Cellulose Insulation: Cellulose insulation is made of shredded newspaper with an added fire retardant. Two relevant properties of shredded newspaper are as follows: (1) without special treatment it will burn; and (2) it naturally absorbs moisture from the air. This can result in the cellulose insulation losing its added fire retardancy as it ages. Cellulose insulation that is saturated because of a flood or other catastrophic event can lose its fire retardants, and even if it can be dried, it should not be reused without consulting the product’s manufacturer. In addition, studies conducted in Canada, New England, and Ohio demonstrated that wet-spray applications of cellulose insulation do not achieve their advertised R-value until dry and may take as long as two months to dry. In many cases, wet-spray applications may need to remain uncovered until completely dry.  

Natural Convection

Natural convection is a form of heat flow in which thermal gradients cause bulk air flow. When air is heated, it expands, becomes less dense, and moves in an upward direction. Generally, natural convection has no effect on insulation performance.

Fiber Glass Insulation: Properly installed fiber glass batts and rolls are not affected by natural convection. In addition, in cold climate conditions, all fiber glass insulations experience improved thermal performance as the temperature in an attic drops. However, some lighter density loose-fill fiber glass products are affected in limited applications such as those found in extremely cold weather environments. In those climates, denser loose-fill insulation designed for extreme temperatures should be installed.

Cellulose Insulation: Natural convection will not affect the thermal performance of properly installed cellulose insulation due to the way the fibers nest together.  

 

Impact of Weight

When installing insulation above ceilings, homeowners should consider the weight of the insulation on the ceiling structure of the home. This is primarily an issue in cold climates where R-values of 38 and higher are commonplace.

Fiber Glass Insulation: Fiber glass insulation is extremely efficient and gives a higher insulating value per pound of insulation installed. Homeowners can install fiber glass insulation up to R-70 over ½ inch ceiling drywall with framing spaced 24 inches on centers without causing drywall to sag.

Cellulose Insulation: Based on U.S. Gypsum weight limit recommendations for back loaded standard drywall and the installed density of shredded newspaper insulations, cellulose insulation may cause ceiling drywall to sag at high R-values when installed over ½ inch ceiling drywall with framing spaced 24 inches on centers.  

Air Leakage

Air infiltration and exfiltration are the uncontrolled leakage of air into and out of a home. It is driven by wind, temperature differences, or HVAC equipment-induced pressures.

If a wall cavity has been properly closed off using drywall, sheathing, and caulking, very little air will flow through it regardless of the type of insulation used. Openings for wiring runs, light switches, and electrical outlets where air infiltration can occur can be sealed with foam sealants, caulking, or foam gaskets. To control air leakage in a home, a house-wrap or other air infiltration control strategies should be considered to limit air infiltration through cracks and joints.

While some debate which insulation products are better at reducing air infiltration, research shows that air infiltration is dependent on the sealant package, and not the insulation type installed in the wall cavity.

A 1997 study conducted by the National Association of Home Builders (NAHB) Research Center for the U.S. Environmental Protection Agency’s Energy Star Homes Program could find no relationship between the type of insulation used and the amount of air infiltration. The study determined that the individual air sealing practices of the insulators had a larger impact on air leakage than the insulation products themselves. These findings were confirmed by a 1997 study conducted by a researcher at Penn State University and a 1996 study by a St. Louis, Missouri utility company.

Fiber Glass Insulation: Minimizing air leakage is dependent on the sealant package and has very little to do with the insulation. The purpose of insulation is to provide thermal performance.

Cellulose Insulation: Despite claims that wet-spray cellulose eliminates air leakage, the research shows that what is in the cavity of the wall or attic – fiber glass or cellulose – has little, if any, effect on air infiltration.

Insulation for Sound Control

In general, the density of the insulation material in a sidewall assembly has little, if any, effect on the Sound Transmission Class (STC) rating of the assembly. STC ratings are a measure of the effectiveness of a given partition construction in reducing airborne sound transmission.

Insulation thickness, however, has a more significant effect on STC ratings than does density. In comparison testing, representative 2 x 4 and 2 x 6 wood stud and metal stud walls demonstrated equivalent or slightly better performance for fiber glass over cellulose when the cavities were completely filled. 

Fiber Glass Insulation: Fiber glass insulation significantly reduces sound transmission in wall, ceiling, and floor assemblies. The first inch of fiber glass insulation can increase the STC value by 3 or 4 points in some constructions. Each additional inch of fiber glass insulation increases the STC value from 1 to 2 points.

Cellulose Insulation: Cellulose insulation is also considered a good insulator against unwanted sound in wall and ceiling assemblies.  

 

Use of Recycled Materials

Increased attention has been given to recycling and recycled products as concerns about our environment have heightened. Both fiber glass and cellulose manufacturers use significant amounts of recycled materials in the manufacture of their products.

Fiber Glass Insulation: Between 1992 and 2008, the fiber glass insulation industry recycled over 18 billion pounds of pre- and postconsumer glass containers, eliminating the need for millions of cubic feet of landfill space. Many fiber glass insulation manufacturers have plants that use up to 40% or more recycled materials in their products. The current industry average is 30% recycled content. Manufacturers are currently exploring ways in which their use of recycled materials can be increased without compromising the performance of their insulation products.

Cellulose Insulation: Cellulose insulation is generally made up of about 80% recycled newspaper and 20% fire-retardant chemicals. Three times more cellulose material by weight than fiber glass is needed to insulate a typical home. An average 1,200 square foot attic insulated to R-38 with cellulose insulation would introduce 300 pounds of fire-retardant chemicals into the home.  

 

Installing Insulation

Building Insulation - Performance Comparison

DOE R-Value Recommendations

Places to add Insulation for $ Savings and comfort

25 Checkpoints for Inspecting Insulation Jobs

Installation Guide - Fiber Glass Loose Fill Insulation

Air Infiltration - Myths and Realities