Fiber Glass vs. Cellulose Insulation

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 Insulation Cellulose 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 Insulation Properly 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

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 Insulation Fiber 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 Insulation Convection 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 Insulation Fiber 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 Insulation Based 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 Insulation Fiber 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.