Comparing Fiber Glass and Cellulose Insulation

Compare Fiber Glass & Cellulose Insulation

Comparing Fiber Glass and Cellulose Insulation

Compare Today, Insulate and Save Tomorrow

IntroductionWhether your pocketbook or the planet is your chief concern, energy effciency can add up to a lot of savings. Reducing energy demand reduces the amount of fossil fuel combustion needed to heat and cool homes, which in turn decreases the amount of carbon dioxide emitted into the atmosphere. In terms of your pocketbook, reducing your energy consumption means lower utility bills. While there are many things you can do to increase your home’s energy effciency, one of the most inexpensive ways is to install additional insulation.

Before Choosing Your InsulationThings to consider when choosing an insulation product include ease of application, thermal performance and value. However, you should also consider the overall lifetime performance of an insulation product as well as its related safety aspects prior to purchase and installation.

A Side by Side ComparisonOne way to compare insulation products is to do a side by side comparison. Here we compare the two most common types of insulation: fiber glass and cellulose. The following comparison reveals important differences between the two products which you should consider before making a final decision.


The thermal resistance of insulation is designated by R-value. R-value is resistance to heat ?ow - 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) in 1980 established a rule which mandates that specific R-value information for home insulation products be disclosed in certain ads and at the point of sale. The purpose of the FTC R-value disclosure requirement for advertising is to prevent consumers from being mislead by certain claims which have a bearing on insulating value. When insulating a home, it’s important that the homeowner gets the R-value speci?ed and that the thermal performance lasts over time.

Fiber Glass Insulation
The R-value per inch of fiber glass insulation can vary depending on the density. Fiber glass batts and rolls, both faced and unfaced, have R-values printed on them. Standard ?ber glass batt insulation has an R-value per inch of approximately 3.0. Most fiber glass manufacturers offer high-performance insulation products that yield a higher R-value per inch (4.0+). However, in nearly all applications, the overall R-value speci?ed is what counts, not the R-value per inch. It’s also very important that the R-value does not deteriorate. The R-value of ?ber glass does not deteriorate over time.

Cellulose InsulationCellulose insulation manufacturers promote the product’s “higher R-value per inch” as making it a better value than fiber glass. Higher R-value per inch is not important in selecting insulation material. It is an advantage only in areas with little space for insulation. In those particular applications, fiber glass high density insulation (R-13 and R-15 batts) provides higher R-value per inch than cellulose.


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

Fiber Glass InsulationProperly installed fiber glass batts and rolls do not settle. Some fiber glass loose insulation may settle over time (usually around 1 percent). This settling does not alter the thermal performance of fiber glass insulation.  When manufacturers’ installation procedures are employed, fiber glass insulation maintains its thermal performance for the life of the building

Cellulose manufacturers agree that their products settle over time. Most set the settling rate at about 20%. Therefore, if cellulose is mistakenly installed to its labeled settled thickness, it may lose about 20% of its R-value when it settles. When the product is not labeled for installed thickness, the Insulation Contractors Association of America (ICAA) recommends that an additional 25% of thickness be added above the labeled settled thickness.


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

Cellulose Insulation 
Cellulose insulation is made of shredded newspaper and will absorb moisture. Also, if soaked, cellulose will “mat” downand thermal performance can be permanently reduced. Assuming existing cellulose does dry after becoming wet, there is a concern that the ?re retardant chemicals may “wash away” leaving insulation materials insuf?ciently protected. 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, wetspray applications may need to remain uncovered until completely dry.

Fiber Glass Insulation
Insulation made of fiber glass is not absorbent. If exposed to moisture, it will not wick
up and hold water, thus it resists any permanent loss of R-value. If fiber glass insulation becomes saturated as the result of flooding or other events not related to actual product use, it should be removed and replaced.


Convection is a form of heat low in which heat is transmitted by air currents. When air is heated, it expands, becomes less dense and moves in an upward direction. Generally, convection has no effect on insulation performance.

Fiber Glass InsulationFiber glass batts and rolls are not affected by convection. However, some lighter density loose-?ll ?ber glass may be affected slightly in limited applications such as those found in extremely cold weather environments. Laboratory attic tests have shown that loose-?ll products experience improved thermal performance as the temperature in an attic drops, but that some light density loose products then may see a reduction in thermal performance as attic temperatures drop further.

Cellulose InsulationConvection will not affect the thermal performance of cellulose due to its heavy density.


When installing insulation above ceilings, homeowners should take into consideration the impact that the insulation weight can have on the ceiling structure of the home. The impact
of weight is primarily an issue in northern climates where R-values  of 30 and higher are commonplace.

Fiber Glass InsulationFiber glass insulation is extremely thermally effcient, yet light in weight. Homeowners can install fiber glass insulation up to R-70 over 1/2? ceiling drywall with framing spaced 24? on centers without causing drywall sag.

Cellulose InsulationBased on U.S. Gypsum weight limit recommendations for backloaded standard drywall* and the installed density of shredded newspaper insulations, there is potential for ceiling drywall to sag at R-values above R-30 for regular cellulose insulation when installed over 1/2? ceiling drywall.


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

Fiber Glass InsulationFiber glass insulation is made from sand and other inorganic materials which are melted and then spun into ?ber glass. Fiber glass is naturally noncombustible and remains so for the life of the product. It requires no additional retardant chemical treatments. Unfaced ?ber glass insulation also is recognized by building code groups as an acceptable ?re stop in residential wood frame walls. Most kraft and foil facings available on some fiber glass insulation are themselves combustible. Products with such facings are intended for non-exposed applications and should not be left exposed. When properly installed, these products do not pose a hazard.

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

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