Differences: Cellulose, Fiberglass and Foam Insulation

Cellulose and Fiberglass Insulation

Cellulose insulation is recycled paper, mostly from newsprint. Fiberglass is tiny strands of glass. Insulating power comes primarily from air spaces between the fibers of the material. Insulating power is reduced when the insulation’s air spaces are compressed. Insulating power declines over time as the material settles under its own weight. Wind and air pressure force outside air through wall and ceiling cracks and openings, allowing heat, sound, moisture, dirt and allergens to be transported by outside air, through the insulation’s porous air spaces and into interior living areas. Government tests show that air leakage through walls and ceiling is responsible for about 40 percent of annual air conditioning and heating costs. Cellulose and fiberglass do not stop air leakage. Performance is typically less than published R-Values because laboratory tests of insulating power do not consider heat transfer due to air movement, settling and imperfect installation fit. Dirt and moisture carried into insulation’s air pockets with outside air create breeding conditions for mold, mildew and bacteria. Outdoor and indoor air pressure differences can eventually force harmful organisms into interior living spaces. “Stabilized” cellulose includes water to make the paper fibers more rigid. And no, we’re not making this up. Naturally, moisture combined with inevitable particle matter from the outside air means greater potential for mold, mildew and bacteria growth. Fiberglass batts do not fit perfectly into spaces between wall studs and ceiling joists. A two percent gap can reduce effective R-Value by as much as 23 percent. Attic air space is not insulated because the insulation can only be placed between ceiling joists on the “floor” of the attic. Attic air temperatures can reach 150 degrees or more during the summer. Very hot attic air greatly reduces the efficiency of air conditioning ducts. Heat stored in the attic insulation’s air spaces during the day steadily flows into the ceiling and radiates into the interior living spaces below throughout the late afternoon and evening hours. Occupants experience a “clammy” feeling. Cellulose is heavy and can cause the ceiling drywall to sag if improperly installed. Imagine dozens of piles of old newspapers laying directly on top of your ceiling, between the framing joists. Cellulose and fiberglass insulation do not contribute to the strength of a building’s walls or roof.

Spray Foam Insulation

Spray foams are plastics like polyurethane and may include agricultural products, like polyols refined from castor beans. Closed cell insulating power comes primarily from the material. Insulating power of open cell spray foam comes primarily from thousands of tiny trapped air pockets. Spray foam insulation does not shrink or change shape once it has expanded and set. Spray foam insulation expands when applied, filling and sealing even the tiniest cracks and openings. This virtually eliminates air movement through exterior walls. Because air leakage is virtually eliminated, the 40 percent of air conditioning and heating costs attributable to air leakage can also be eliminated. Performance typically exceeds published R-Values because laboratory tests of insulating power do not consider heat transfer due to air movement, which spray foam blocks. Solid barrier means no pathways through insulation for dirt or moisture to accumulate. No conditions for mold, mildew and bacteria to grow. Closed cell spray foam insulation forms a solid barrier against moisture. Open cell spray foam insulation will absorb vapor but dissipates the moisture within a short period of time. Spray foam insulation expands to fill any space, regardless of dimensions, shape or surface irregularity. Attic air space is insulated because insulation can bond to the underside of the roof sheathing. Attic air space stays as much as 40 percent cooler during the summer. Much cooler attic means air conditioning ducts operate much more efficiently. R-Values do not measure this effect. The attic is much cooler because the insulation is above the attic rather than below it. Late afternoon and evening heat radiation from the ceiling into interior living spaces is substantially reduced. Occupants feel much more comfortable. The weight of spray foam insulation is not significant, and it does not lay on top of your ceiling in any case. Closed cell spray foam insulation can double the strength of walls. Adhesive spray foam can increase the strength of your roof by as much as 275 percent.