Cellulose, Fiberglass and Foam Insulation
We know what you’re thinking: Everybody says their insulation is best. Sorting out competing product claims can be difficult with any product and it’s even tougher when you’re dealing with complicated subjects like building science and heat energy transfer.
Choosing an insulation system for your home is a big decision that will impact your energy costs, comfort and air quality for years to come. The side-by-side comparison chart below explains the basic differences between spray foam insulation and the two “fiber” products: cellulose and fiberglass.
|Cellulose and Fiberglass Insulation||Spray Foam Insulation|
|Cellulose insulation is recycled paper, mostly from newsprint. Fiberglass is tiny strands of glass.||Spray foams are plastics like polyurethane and may include agricultural products, like polyols refined from castor beans.|
|Insulating power comes primarily from air spaces between the fibers of the material.||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.|
|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.||Spray foam insulation does not shrink or change shape once it has expanded and set.|
|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.||Spray foam insulation expands when applied, filling and sealing even the tiniest cracks and openings. This virtually eliminates air movement through exterior walls.|
|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.||Because air leakage is virtually eliminated, the 40 percent of air conditioning and heating costs attributable to air leakage can also be eliminated.|
|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.||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.|
|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.||Solid barrier means no pathways through insulation for dirt or moisture to accumulate. No conditions for mold, mildew and bacteria to grow.|
|“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.||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.|
|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.||Spray foam insulation expands to fill any space, regardless of dimensions, shape or surface irregularity.|
|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.||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.|
|Very hot attic air greatly reduces the efficiency of air conditioning ducts, which typically run through the attic in Florida homes.||Much cooler attic means air conditioning ducts operate much more efficiently. R-Values do not measure this effect.|
|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.||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.|
|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.||The weight of spray foam insulation is not significant, and it does not lay on top of your ceiling in any case.|
|Cellulose and fiberglass insulation do not contribute to the strength of a building’s walls or roof.||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.|
|Cellulose and fiberglass attic insulation have no affect on the cost of your homeowners insurance.||State-approved spray foam attic insulation products can reduce Florida homeowners insurance cost by 25 to 60 percent.|
What’s an R-Value?
R-Value is a indicator of an insulation product’s ability to block heat energy transfer. The R-Value for open cell spray foam insulation is roughly equal to the R-Values for cellulose and fiberglass. The R-Value for closed cell spray foam insulation is significantly higher.
It’s important to remember that published R-Values for different insulation products simply reflect the insulation’s ability to stop heat transfer under apples-to-apples laboratory test conditions. Much like mileage ratings for automobiles, R-Values cannot tell you how much better or worse different insulation products will perform when a 10 mph wind is blowing, or when fiberglass batts have been crammed into a smaller space than they are designed for—compressing their air pockets and reducing their effectiveness.
And it’s impossible for R-Values to account for the single biggest difference between spray foam insulation and cellulose or fiberglass insulation: the huge reduction in attic air temperature because of the location of the insulation—spray foam insulation bonds to the underside of the roof sheathing, above the attic air space. Loose cellulose or fiberglass and fiberglass batts can only lay between ceiling joists on the “floor” of the attic.
Laboratory tested R-Values for spray foam insulation are comparable to (open cell) or better than (closed cell) the R-Values for cellulose and fiberglass insulation. When you consider real world factors, though, there is no comparison. Spray foam insulation is clearly the superior choice for home and building insulation.