| Fiber Glass Insulation | Cellulose Insulation |
| Fiber glass insulation is not corrosive and contains no chemicals that can corrode pipes and wires. | Certain chemicals routinely applied as a fire retardant to most cellulose insulation (particularly the sulfates) can cause the corrosion of pipes and wires under some conditions. |
| Fiber Glass Insulation | Cellulose Insulation |
| Fiber glass insulation is made from sand and other inorganic materials which are melted and then spun into fiber glass. Fiberglass is naturally noncombustible and remains so for the life of the product. It requires no additional fire-retardant chemical treatments. | 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 Council (CPSC). To protect against fire hazards, cellulose insulation is heavily treated with fire retardant chemicals prior to installation. Tests 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. That's the surface temperature of a 75watt light bulb. |
| Fiber Glass Insulation | Cellulose Insulation |
| Fiber glass insulation is one of the most thoroughly tested building materials in use today. The great amount of medical scientific evidence compiled over more than sixty years by industry, government and independent research organizations supports the conclusion that fiber glass insulation is safe to use when manufacturers' recommended work practices are followed. | Questions about the health and safety aspects of cellulose insulation persist in the building industry because comprehensive medical scientific testing of the products has never been conducted. Repeated requests by union and contractor groups that such testing be undertaken have been ignored. Given the high levels of exposure measured during cellulose installation, only after long-term experiments are available will it be known if cellulose insulation is safe to use. |
| Fiber Glass Insulation | Cellulose 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 fiber 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 specified 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 fiber glass does not deteriorate over time. | 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. |
| Air infiltration is the uncontrolled leakage of air into and out of a home. It is driven by wind, temperature differences, or appliance-induced pressures. | |
| Fiber Glass Insulation | Cellulose Insulation |
| Properly installed fiber glass insulation in a wall cavity matches cellulose in combating heat loss from air infiltration. Minimizing air infiltration is dependent on the sealant package, not the insulation. The purpose of insulation is to provide thermal performance. | Despite claims that wet-spray cellulose eliminates air infiltration, the research shows that what's in the cavity of the wall or attic - fiber glass or cellulose - has little, if any, effect on air infiltration. |
| Convection is a form of heat flow 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 | Cellulose Insulation |
| Fiber glass batts and rolls are not affected by convection. However, some lighter density loose-fill fiber glass may be affected slightly in limited applications such as those found in extremely cold weather environments. Laboratory attic tests have shown that loose-fill products experience improved thermal performance as the temperature in an attic drops, but that some light density loose-fill products then may see a reduction in thermal performance as attic temperatures drop further. | Convection will not affect the thermal performance of cellulose due to its heavy density. |
| Fiber Glass Insulation | Cellulose Insulation |
| Properly installed fiber glass batts and rolls do not settle. Some fiber glass loose-fill 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, fiberglass insulation maintains its thermal performance for the life of the building. | Cellulose manufacturers agree that their products settle overtime. 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. |
| Fiber Glass Insulation | Cellulose Insulation |
| Fiber glass insulation is extremely thermally efficient, yet light in weight. Homeowners can install fiber glass insulation up to R-70over 1/2 inch ceiling drywall with framing spaced 24 inches on centers without causing drywall sag. | Based on weight limit recommendations for back loaded 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 inch ceiling drywall with framing spaced 24 inches on centers. |
| Fiber Glass Insulation | Cellulose 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. | Cellulose insulation is made of shredded newspaper and will absorb moisture. Also, if soaked, cellulose will "mat" down and thermal performance can be permanently reduced. Assuming existing cellulose does dry after becoming wet, there is a concern that the fire retardant chemicals may "wash away" leaving insulation materials insufficiently 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, wet-spray applications may need to remain uncovered until completely dry. |