Fiberglass Insulation vs. Foam

One of the most hotly contested debates in the world of attic insulation is the question “fiberglass or spray foam?” Whereas fiberglass has been a classic go-to staple insulated in American homes for several decades now, spray foam is the en vogue new kid in the neighborhood generating all the latest buzz.

But does spray foam truly have what it takes to dethrone fiberglass as the top choice for attic insulation installation among homeowners?

Answering this question requires a closer look at both fiberglass insulation vs foam. What exactly are they? How are they different from one another? And most importantly, which one best suits both your budget and specific needs for your unique attic? Read on for a tale of the tape.

What is Fiberglass Insulation?

First up in the fiberglass insulation vs foam debate is fiberglass. Fiberglass is a series of extremely delicate fibers comprised of various recycled materials, primarily-you guessed it!-melted down glass. These glass fibers are frequently held together by adhesive backing that serves as a vapor barrier such as reflective aluminum foil or paper.

Cheap but undeniably effective as an insulator, fiberglass is used by roughly 85% of American homeowners today.

How is Fiberglass Packaged?

Fiberglass is available for purchase in the following two forms: wildly popular batts (i.e. the large blankets that bear a striking resemblance to cotton candy) and less common blown-in loose-fill.

Here’s a closer look at both:

  • BattsFiberglass Batts has become a favorite with homeowners due to the fact that they’re simultaneously large and light. They’re very easy to pick up at the store and carry upstairs, and once they’re unrolled, they’re able to cover a ton of space. And as an added perk, they’re often designed to be the exact same size as the standard spacing between studs on attic walls.

The only problem with fiberglass batt is that, in attics that have either cumbersome obstructions on the ground and walls or feature awkward spacing, it must be cut precisely to size. Cutting them too short will leave major gaps in coverage for air to flow through while leaving them too long results in irregular compression. And both are bad news for your monthly heating and cooling costs.

Unfortunately, because fiberglass is so light in nature, customizing batts can be not only a total pain but also a costly misstep when done incorrectly. Thus, even if you’re a DIY type of person, you should still call on a professional installer to set up your batts and avoid the unnecessary high fiberglass insulation cost in the long run. This is especially true if your attic is marked by obstacles and irregular space between joists.

  • Loose-Fill – Fiberglass is also available for purchase in bags as loose-fill material, which comes in large chunks. Installing this loose-fill fiberglass in your attic entails a professional installer using a large blowing machine (or you renting the machine if you’re feeling particularly ambitious) to spread the fiberglass wherever necessary.

Blowing in loose-fill fiberglass is a great choice for homeowners who live in older buildings with prior insulation in place and multiple obstructions in the way, as it’s perfect for filling in the tight voids around pipes and wiring that batts struggle to cover.

And since the blowing machine eliminates the need for maneuvering around the room during installation, loose-fill insulation is also a prime choice for any attic with a tight space and low ceiling.

What is Spray Foam Insulation?

Spray foam insulation is a liquid chemical that comes out of a spray can and expands to form an airtight seal over cracks and any other voids that air could flow through.

How is Spray Foam Packaged?

Spray foam comes in two varieties:

  • Open Cell – This refers to foam comprised of cells that aren’t fully enveloped, which makes the foam both flexible and soft.
  • Closed Cell – As the name suggests, this is foam with cells that are completely closed off. These cells press up against one another to block the passage of air and moisture. As a result, closed cell spray foam is more rigid, stable and dense than its open cell counterpart.

Between the two, closed cell spray foam is easily the better insulator, especially in attics where space is tight. Plus, its moisture-resistant qualities make it an ultra-stingy vapor barrier that’s impervious to water damage.

The downside with closed cell foam is that, because it’s significantly more capable than open cell foam, it’s naturally much costlier. And price tag aside, open cell foam definitely has its own merit. Its ability to expand makes it a prime choice for attics with hard to reach nooks and crannies. Additionally, in cases when a single application of foam can fill the entire space between studs, open cell foam is the better option for soundproofing.


Deciding which type of insulation is the best fit for your attic begins and ends with an understanding of insulation R-value, the measurement used to determine an insulator’s effectiveness in resisting airflow. R-value is a simple “the higher, the better” statistic.

On paper, spray foam is the clear winner in this category, as closed cell foam can reach staggering R-value heights of up to 7.0.  It also doesn’t sag or settle over time, a side effect that fiberglass insulation suffers from when it’s installed incorrectly.

But fiberglass is no slouch at blocking airflow either, as specially designed medium and high-density fiberglass have R-values as high as 4.3. It’s also important to note that, while there’s a limit to how many applications of foam you can spray in one area, the delicate and versatile nature of fiberglass gives you several options for stacking batts upon one another for boosted insulation.

Resistance to Moisture

This category is a neck-and-neck race. Both spray foam and fiberglass are adept at resisting moisture, which means you’re never going to see mold and mildew growing on it either. This makes both invaluable options for homes located in particularly humid regions.

Round Three: Longevity

This is yet another category where both foam and fiberglass are in a class by themselves.

In attics that can maintain ideal conditions, fiberglass insulation will last for a remarkable 100 years. Spray foam, on the other hand, will tap out at about 80 years, which is certainly nothing to scoff at, but still comes short of the century mark gold standard set by fiberglass.

Additionally, though foam neither sags nor settles the way improperly installed fiberglass can, it does tend to shrink over time, a drawback you don’t have to worry about with fiberglass insulation in the attic.

The Installation Process

While you’re deciding on the home insulation material, it helps to look at other aspects, like insulation installation.

Fiberglass runs circles around spray foam in this category.

In wide-open attics with no obstructions on the walls or ground and consistent spacing between joists, the installation of batts couldn’t be simpler for your installer (or you, if you’re the DIY type). Even for attics with prior insulation or multiple obstructions that call for loose-fill fiberglass, using a blowing machine is a relatively straightforward and inexpensive process.

Conversely, the installation of spray foam is a double-edged sword. As discussed above, applying spray foam incorrectly can have grave health consequences, a scary thought given the fact that spraying foam is a complicated process even for professionals.


Both foam and fiberglass share two distinct intangibles that not all other insulators can match:

  • Fire-Resistance – They’re noncombustible, which means that you can set either up between the wooden joists in your attic without ever having to worry about them catching fire.
  • Sound Barricade – They stand at the top of their class in blocking both inside and outside noise, giving the acoustics in your home a natural boost.


When it comes to choosing insulation materials for your attic, perhaps the only consideration more important than R-value is standalone value, and understanding insulation installation costs.  In both the short-term and the long run, which material truly gives you the most bang for your buck?

When you factor in cost, you can argue that fiberglass gives you a better immediate payoff. While spray foam’s top-notch thermal performance costs you an arm and a leg, fiberglass provides you with a similarly impressive output for only a fraction of the cost.

Because both foam and fiberglass are superstars at trapping air, both will save you considerable money over time on your energy bill. But fiberglass may also have a leg up on foam in long-term value because of its energy efficiency as it conserves 12 times as much energy as it generates, a unique trait that can slash your utility bill by a whopping 40% annually!

The Final Scorecard

There’s no denying that spray foam is the top dog insulator on the basis of sheer R-value. But choosing the best insulation for your specific attic isn’t as simple as just picking the material with the highest R-value on the packaging. You also have to consider crucial factors like:

  • The amount of space in your attic
  • The climate in your region
  • Potential safety hazards
  • And most importantly, your overall budget.

All things considered, fiberglass will be the best choice for most attics, especially attics in brand new buildings or renovation projects that don’t have HVAC units on the floor or pipes nestled on the walls. The benefits of fiberglass insulation make it clear why time and time again, this is a popular choice for insulating attics. Fiberglass comes close to matching spray foam in all major performance categories, its quick and simple installation is the opposite of the complete nightmare of spray foams’, and—the knockout punch—it’s as cheap as spray foam is expensive.

Though spray foam has a lot to offer, it’s with good reason that the walls and roofing of a vast majority of attics in American homes will continue to look like cotton candy.

Call on Attic Construction for All Your Fiberglass Installation Needs

Think you’ve decided on the best insulation for your attic and are ready for installation? Since attic and home insulation is a crucial part of any house, it’s best to skip the DIY on this one and call a professional. Much like fiberglass itself, our expert staff at Attic Construction provides you with the best for less: outstanding service at rates that can’t be beat.

Whether you’re looking for guidance on how to install fiberglass batts yourself or want to put the job in the hands of pros that you can guarantee will do it right, we’re here and ready to help with any and all of your attic insulation needs.

Contact us for a free estimate today!


1) “Fiberglass Insulation vs. Spray Foam Insulation” by Editorial Staff at Diffen

2) “4 Pitfalls of Spray Foam Insulation” by Allison Bailes

3) “Everything You Need to Know About Insulation’s R-Value” by editorial staff at Today’s Homeowner with Danny Lipford

4) “How Long Will Fiberglass Insulation Last?” By SF Gate,usually%20stated%20as%20100%20years.

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