Spray Foam Vs Fiberglass: Two Insulation’s Duke It Out for Champ Status


In this corner, weighing in at ½ lb. to 4 lbs. per cubic foot, new kid on the block and up-and-comer — spray polyurethane foam insulation. And in this corner, king of the  insulations  and industry standard for decades —  fiberglass . In the battle to determine which building insulation is the better value for money, which one wins? The answer may surprise you.

Many people wonder how spray foam and fiberglass compare. Usually, what they really want to know is how much more expensive spray foam is. Phrased another way, which building insulation is the better value for money? The answer is always the same: spray foam and fiberglass can’t be compared, price-wise or in any other way. That’s because these two insulations are completely different products that work on different principles.

Let’s take a deeper look…

ROUND ONE: Fiberglass as Insulator

 Fiberglass   insulation  has been the industry standard insulation for decades because it’s usually easy to install, quick to put in place, and relatively inexpensive. Sure, it’s a decent insulator, doesn’t significantly add to building costs, and can be retrofitted easily and inexpensively for existing buildings. But while fiberglass has been the big man on campus for a long time, it doesn’t solve all of a building’s energy problems. That’s where spray polyurethane foam comes in. More on that in a minute, but first let’s touch on which is perhaps the number one problem plaguing most buildings today: air leakage.

Eliminating air flow is critical to a building’s overall energy efficiency and creating a high-quality building envelope. But because traditional forms of  insulation , including  fiberglass , are not air barriers, wherever these types of  insulations  are installed, approximately 40-50% of an energy bill is related to air leakage. That’s a lot of money and energy being wasted.

Fiberglass, in other words, is an insulator only. It does little, if anything, to combat air leakage.

ROUND TWO: Spray Foam as Insulator and Air Barrier

Air leakage may not sound like a big deal at first. What’s the harm in having a few cracks here or there, right? That might not sound like a catastrophe, but consider that the average building has more gaps and crevices than you might think: windows and doors are biggies, as are floors, walls and ceilings, but don’t forget about recessed lights, plumbing penetrations, fireplace flues, electrical outlets, vents and fans, attic hatches, wall air conditioners, mail slots…the list could go on and on. Adding all those areas up amounts to approximately 60% of the air in a building being lost through a leaky building envelope.

Spray polyurethane foam to the rescue. Spray foam is two products in one. Because it’s spray applied, it fills every nook and cranny and hole and crack and crevice, thus eliminating air leakage. Partner this with a high R value, and you’ve got yourself a product that solves two major problems that exist in buildings today: insufficient insulation and air leakage.

Spray foam, in other words, is an insulator and air barrier. Now compare this to fiberglass that only insulates. Foam offers something that fiberglass can’t, an extra benefit that comes standard, like power windows in a car. Fiberglass will never be an effective air barrier, whereas foam by its very nature is an air barrier. Now do you see how these types of insulations can’t be compared?

ROUND THREE: The Price Comparison

So when faced with the inevitable question, “Is spray foam more expensive than fiberglass?” we always say, “Well, yes, of course.” That’s because foam offers additional benefits that fiberglass can’t. Wouldn’t you expect to pay more for a product that offers more benefits? It’s like asking if a car with power windows is more expensive than a car with manual crank windows. Unless the car with manual windows has other amenities not available in the car with power windows, the power window car will be more expensive.

So how much more expensive is spray foam over fiberglass? Usually about twice as much. That’s a hard pill to swallow for a lot of people on a tight budget, or otherwise fearful of outlaying twice as much money upfront for a product they’ll probably never see. But it’s important to keep this in mind: spray foam is a permanent once-and-done insulation, so while you’re paying more upfront for it, it’ll last the lifetime of your building and will never need to be updated. Plus, the money you pay upfront will come back to you over time in the form of a less expensive utility bill every month. Remember that spray foam is an air barrier, so the 40-50% of your utility bill associated with air leakage will be eliminated. That’s a huge bonus compared to traditional  fiberglass   insulation .

So in the battle of spray foam vs. fiberglass, fiberglass still has a place in the market for its inexpensive ability to insulate quickly (yet not permanently). But if you’re looking for a product that offers more, in the form of air leakage protection and increased savings on utility bills, spray foam is the champ.