Q: What are the differences (pros and cons) between fiber glass and cellulose insulation?
A: There are three important differences between fiber glass and cellulose.
- Fire Resistance - Fiber glass is made mostly of inorganic materials and therefore is naturally non-combustible and has a low flame spread rating. It will maintain its fire resistance over its lifetime. On the other hand, cellulose is made up of newspaper, which is organic and naturally flammable. Therefore, approximately 20% of the finished cellulose product is comprised of fire retardant chemicals (80% newspaper / 20% fire retardant chemicals). These fire retardant chemicals may not be applied consistently and may deteriorate over time. Smoldering and re-kindling of fires have been reported with this product.
- Moisture Absorption - fiber glass is installed dry and does not absorb or retain moisture. Cellulose is often installed damp and needs to fully dry after installation. Even after drying, cellulose can absorb moisture, which can lower the R-value of the product and may promote fungal growth.
- Settling - Fiber glass has nearly no settling (1-3%). Therefore, the R-value is stable over time. Cellulose can settle or shrink causing the R-value to deteriorate over time. Unless 20% or more extra thickness is installed, you can't be sure of achieving the desired R-value.
Insulation Material Comparison Summary: Fiber Glass vs Cellulose
|
Performance Property |
Fiber Glass |
Cellulose |
|
Thermal Resistance |
Variety of R-values available in batts, and loose-fill. Stable over time. |
Higher loose-fill R/inch (for tight spaces). R can deteriorate from settling/shrinkage. |
|
Ease of Installation |
Batts install fast, except careful cutting, fitting required in irregular spaces. Loose-fill requires equipment and skilled installer. |
Equipment maintenance and skilled installer required. Voids unlikely with careful installer. Cleanup takes time. |
|
Moisture |
Installed dry. Low moisture adsorption. |
Often installed damp. Should be allowed to dry. Absorbs moisture which lowers R-value and may promote fungal growth. |
|
Air Flow |
Filled cavities restrict air circulation. (Infiltration controlled by other measures.) |
Likely has higher air flow resistance depending on installation. (doesn't effect home's main leakage points) |
|
Attic Convection |
Batts not susceptible. Loose-fill slightly impacted in some climates. (Example: $3.92/1500 sq.ft. attic effect in Denver, Colorado) |
Not susceptible at traditional densities. |
|
Corrosion |
Non-corrosive |
Corrosion a concern with retained moisture and some fire retardants. |
|
Fire Resistance |
Non-combustible, low flame spread |
Combustible. Fire retardant treatment may not be consistent. Smoldering and re-kindling of fires reported. |
|
Environmental Benefits |
25% recycled glass, and light weight so relatively fewer resources consumed. Energy savings is big environmental plus. |
80% recycled paper but 20% virgin chemicals. More resources consumed. Energy savings is big environmental plus. |
|
Health Impacts |
Skin/respiratory irritation possible. Long-term effects have been extensively studied and safe practices defined. |
Allergic effects possible from inks, dust, chemicals. Long-term effects never researched but questions persist. |
