Spray Foam Insulation vs Fiberglass

Spray Foam Insulation vs Fiberglass

In the world of attic insulation, the debate for spray foam vs. fiberglass has been a hotly contested topic. Fiberglass has been the more established, classic insulation method while spray foam has experienced a boost in popularity in the recent past. The buzzworthy topic in the industry has begged the question of whether spray foam is a worthwhile, viable replacement or substitute for the more traditional fiberglass approach.

To answer this question, it is important to understand what exactly each insulation method is, how the two differ from each other, which needs each method better serves, and which of the two is more budget-friendly depending on your particular situation.

Fiberglass Insulation

Fiberglass Insulation

Fiberglass is a material composed of very fine fibers. These are produced from a variety of recyclable materials, with melted down glass being chief among them. These small materials are held together by an adhesive agent such as paper or aluminum foil. This bonding of pieces serves as a vapor barrier, an attribute that makes it an effective insulator, which is very moderately priced, currently used in most American homes.

Fiberglass Packaging

Fiberglass is commonly packaged in the form of batts, the cotton-candy-looking blankets of the insulation material. Somewhat less commonly, it also appears as a brown fill.


Batts are popular with homeowners seeking insulation of their homes because they are light, making them easily portable between rooms and floors, as well as large, with their rolled-out size allowing a wide area of distributed coverage. Even more conveniently, their size is typically cut to fit comfortably between studs to the walls of attics.

However, the size of the batts does present a particular challenge in terms of covering attics that may not be perfectly open or are awkwardly spaced, requiring that the batts be cut precisely to size. If they are too short, they will leave some amount of space uncovered, while being too long results in inconvenient excess resulting in abnormal compression. Neither is particularly favorable to reducing the electric or gas bills, the entire point of insulation.

While fiberglass batts are less costly, customization that some attics would call for can end up being quite costly. It is also a significant pain point to cut them to size depending on the attic layout. If you are a homeowner looking to save money by installing the fiberglass batts yourself, you will be unlikely to reduce fiberglass insulation costs by self-cutting, especially if your attic features a lot of obstacles.


Unlike the fluffy, large sheets of fiberglass in batts, some fiberglass insulation is offered in loose-filled fiberglass chunks, typically packaged in bags. The installation of these loose-filled chunks requires the use of a special insulation blowing machine to distribute the fiberglass evenly across a particular attic surface. This is why it is commonly referred by homeowners as blown in insulation.

Some insulation DIYers choose to rent a machine to help out with this, while others opt to hire a professional fiberglass insulator who owns such a machine, which reduces the necessity to move around in potentially tight and cramped attic spaces.

While batts need to be cut to size to fit obstructive, uneven areas, loose-fill can be easily applied to tight spaces, corners, segregated areas, and other hard to reach places without the hassle of cutting a large fiberglass sheet to do so. It also fits easily over wires and pipes, another area where batts end up struggling to lay out evenly.

Spray Foam Insulation

Spray Foam Insulation

Spray foam insulation is chemically composed to be sprayed into everywhere ranging from open areas to tight nooks. As the foam covers an area, it expands getting into small crevices and corners where traditional fiberglass insulation just cannot reach. This helps to seal the cracks in the wood that could potentially allow air permeation.

Spray Foam Packaging

Spray foam packaging comes in either the open-cell or closed-cell variation. Open-cell foam is soft and highly flexible due to the air bubbles present inside, making this type of spray foam not fully enveloped. The closed-cell, on the other hand, is a near-total seal, with minimal space in the resulting foam. This promotes a far lower rate of air coming in through the more rigid, denser seal. Closed-seal’s dense nature also makes it highly resistant to moisture permeation, which makes it an ideal choice for those parts of the house that contact the home’s exterior, such as attics.

The efficiency of closed-cell foam, however, comes at a price. For one thing, its cost is significantly higher than other insulation variants, but it also expands less than open-cell foam, meaning that it is not as effective at getting into small, tight spaces.

Open cell is a more ideal choice for insulating interior areas (those with no contact with the outdoors). As it can allow moisture to pass through slightly more than the closed-cell variant, its contact with the outside is ideally needing to be minimized. Because it seeps in between studs and fills in all of the little cracks and nooks superbly upon expansion, it more tightly expands over the coverage area. This makes it a great soundproofing option.

Spray Foam Insulation vs Fiberglass Comparison


Insulation is all about keeping air and moisture out. The higher resistance to these elements that spray foam has, the higher its R-value score. The higher the R-value, the more effective the spray foam is at keeping water and air out (or in). Closed-cell foam is among the highest in this regard, able to achieve an R-value of up to 7.0. Unlike fiberglass, it does not settle or sag over time, a common downside of poorly installed fiberglass insulation.

Fiberglass does have one particular advantage over spray foam, however. Spray foam requires one application to cover an area, while fiberglass insulation limitations are significantly less. In other words, if you needed supplemental insulation, you can easily later fiberglass batts on one another.

Moisture Resistance

In terms of moisture resistance, both fiberglass and spray foam are excellent deterrents of mold and mildew, so this is a category that is truly a toss-up between the two. The ability to resist the overwhelming penetration of water makes either a viable option for insulation use.


In terms of longevity, both spray foam and fiberglass are outstanding performers. If you use fiberglass to insulate your attic, unless you want to update it with spray foam, you will likely never need to reinsulate it again. That’s because fiberglass has an astonishingly long lifespan of 100 years.

While it doesn’t quite meet the century mark, spray foam is considered viable for a respectable 80 years, far longer than anyone homeowner will need in their lifetime. Unlike fiberglass that is not administered correctly, spray foam won’t settle or sag over time, but it does shrink gradually, giving fiberglass insulation a slight advantage in this category.


In terms of installing a particular type of insulation, there is no competition. In open attic spaces, few installations are simpler than that of unrolling batts of fiberglass. When no obstructions exist, and the spacing between joists is consistent, the fiberglass batt layout is a very simple process. Even when a machine needs to be used to fill in tighter attic spaces with loose-fill insulation, is simpler than the process of applying spray foam.

While professionals can effectively apply spray foam, it is, after all, a chemically rendered compound, which means if applied incorrectly, could have negative impacts on the health of the applicator or the home’s residents. While it is extremely effective in its performance, it is significantly more challenging to install.

Intangible Benefits

Both fiberglass insulation and spray foam possess two important attributes that make them stand out as the primary facilitators of indoor insulation.

The first is that they are both non-combustible, which means they are fire-resistant. That means that either one can be filled in between wood joists and in an attic, including around electrical boxes, without the concern of them catching on fire.

The second is that they both act as a soundproofing barrier. That means that not only do they reduce external noises from entering, they also supply the indoor space with enhanced acoustic qualities.


One of the main factors that influence the choice for homeowners in terms of insulation is which one is worth the expense. Will the less expensive, longevously, and easier to install fiberglass variation give them the best bang for their buck, or is the higher R-value, more inclusive, more efficient spray foam a better choice?

Fiberglass provides a quality insulation solution that is, in most ways, effectively comparable to that of the most expensive spray foam option, for a significantly lower cost. Both types will save you money in heat and electric bills, as both are effective at trapping air. Fiberglass has been shown to slash energy bills due to its energy efficiency (conserving 12x the energy it generates).


The high R-value of spray foam insulation makes it the dominant insulation solution on the market, but there are more considerations to choosing insulation types than just the R-value alone. A few other factors to consider include:

  • Regional climate
  • Attic space coverage
  • Safety hazards
  • Overall budget

By and large, there is a reason that fiberglass usage continues to dominate the market in terms of how many people utilize it. For attics in most homes, renovated buildings, or brand new constructions that do not have wall nestled pipes or floor-based HVAC units, fiberglass amounts to the better choice.

In most performance categories, fiberglass either matches or nominally trails spray foam insulation. It’s significantly less expensive and the ease of insulation makes it ideal for DYI installers, as well as the budget-conscious ones. It is no wonder that while the benefits of spray foam are quite real, most American homes’ attics are still filled with cotton-candy looking fiberglass insulation.