Insulation: Spray Foam vs. Blown-in Cellulose

Photo credit: mironovm

Insulation can improve your home’s energy efficiency, as insulated spaces provide better temperature control in both hotter and colder seasons. If you’re planning to insulate your home, you want a sustainable, durable, high-quality insulating material. Between spray foam and blown-in cellulose, which is better?

Both spray foam and blown-in cellulose insulation have their advantages. Spray foam has a higher R-value, so it’s the more effective insulator. But cellulose is better at insulating street noise.

In this article, we’ll discuss both spray foam and blown-in cellulose insulation in detail. Then we’ll compare these two insulating materials so you can decide which is the best one for your home. You won’t want to miss it!

What Is Spray Foam Insulation?

First, let’s talk about spray foam insulation.

Spray foam is made of polyol resin and isocyanate. Polyol is a type of hydroxyl compound, while isocyanate is a bonding compound that’s often used in surface coating to produce rigid foams such as spray foam.

When you first apply spray foam, it might not look like much, but it quickly begins expanding. Its liquid volume can increase to between 30 and 60 times more than what it was when you initially sprayed the foam.

The thermal resistance of spray foam insulation is one of its most defining features and the reason so many homeowners flock to it.

Heat can transfer in three different ways: convective, radiant, and conductive heat transfer. Convective heat transfer is when heat occurs somewhere else, such as outside of the home, and then air and water transfer the heat into the home, warming it up.

Radiant heat transfer occurs when heat energy from warm surfaces is then absorbed by less reflective surfaces. Finally, conductive heat transfer is how thermal energy travels between substances when one’s temperature is higher than the other.

Spray foam insulation can halt all three forms of heat transfer, giving it a well-earned high R-value. An R-value is a measurement of how well insulation blocks heat flow.

Here’s a video of a homeowner who chose to have spray foam installed in the attic. A few minutes in, you can watch the spray foam being applied and expanding.

The Types Of Spray Foam Insulation

You can select from two types of spray foam insulation, open or closed. Both terms refer to the state of the cells within the insulation.

Open spray foam has open cells for a malleable, softer spray. If you need to get into tight areas of your attic or an oddly-shaped corner of your basement, open-foam insulation might be the better pick.

Closed-cell spray foam features cells that are sealed shut. Without any moisture or air in the cells, the spray foam has a harder, rigid texture. It’s also better for durability, but you can’t use it in tight spaces.

Spray Foam Pros And Cons

Let’s discuss the pros and cons of spray foam insulation, starting with the pros:

  • You can choose between open or closed-cell spray foam for different applications.
  • Spray foam has a great R-value, since it can block out all three forms of heat transfer.
  • Spray foam is quite easy to apply, especially in tight areas.

Here are some downsides of spray foam insulation to consider:

  • Spray foam has chemicals that can be hazardous if you misuse the product.
  • For each square foot, you can pay up to $1.50 for spray foam, which makes it costlier compared to insulation materials like fiberglass.

What Is Blown-in Cellulose Insulation?

The second insulation material we’re considering is blown-in cellulose. This insulation comes from plant fibers or wood sources. It’s installed within roof cavities and the walls of homes.

The plants that are most often used to produce cellulose insulation are sisal and corn. For commercial insulation, you’re more likely to see blown-in cellulose from wood, including wastepaper, office paper, cardboard, and recycled newspaper. This is energy efficiency at work.

A picture of ground up grey fibers in between building studs, showing what celluose insulation looks like.
Cellulose insulation isn’t pretty. But it can be an eco-friendly way to keep your space comfortable and your energy costs down.

As the name “blown-in cellulose” suggests, the insulation is blown into walls, often before construction is finished. In that regard, you can use cellulose insulation in much the same way as spray foam.

Sometimes a home is already fully built, but the homeowner decides that they want blown-in cellulose insulation. In this case, the job would require drilling a hole into the interior drywall or plaster, or exterior siding. Then a technician would insert a blower nozzle in the hole and fill the hole with cellulose.

After adding the insulation, the technician and their team would patch up the wall so you could barely tell that a hole was ever there.

Some homeowners opt to add blown-in cellulose on top of pre-existing fiberglass batts. That’s likely because besides maintaining the temperature of your home, cellulose is also an excellent sound dampener.

Blown-in Cellulose Pros And Cons

As we did with spray foam insulation, let’s talk about the benefits and downsides of blown-in cellulose. We’ll start with the pros:

  • Blown-in cellulose is fire-retardant, which can put any homeowner’s mind at ease.
  • Cellulose can be “green” if it’s made of recycled wood materials. (Sometimes, though, you might also see the inclusion of borate, a chemical treatment that reduces the overall eco-friendliness of this insulation material.)
  • Besides insulating, cellulose will also reduce outside noises so you can enjoy a more peaceful home.

Here are some potential cons to consider:

  • Cellulose insulation has a slightly lower R-value than both types of spray foam and thus it takes up more space and material to get the same R value as spray foam.
  • You might not like the idea of drilling holes in your walls.
  • Loose insulation can settle to the point where it creates pockets where cold or hot air can enter, making it less effective.

Which Is The Best Type Of Insulation?

Now that you’re clearer on both spray foam and blown-in cellulose insulation, it’s time to discuss which is the better choice for your home.

That depends on the qualities that you care about. For instance, if you want insulation with a superior R-value, that’s spray foam, but only closed-cell spray foam. (The open-cell insulation has an R-value of 3.7 for every inch, which is okay but not amazing.)

Interestingly, blown-in cellulose insulation has an R-value of about 3.5 an inch. Yet with closed-cell insulation, there’s much less of a comparison. This type of spray foam boasts an R-value of 6.5 an inch. That’s twice as good as either cellulose or open-cell spray foam.

If you’re a Florida resident, then paying attention to the R-value of insulation is especially pertinent. You already have enough heat to deal with in your home, and often all year long. You need an insulating material that will redirect or resist heat, and that’s spray foam.

If you want noise reduction with your insulation, then blown-in cellulose could be a winner. This material will insulate your home from sounds such as street noise, the neighbor’s loud barking dog, and people on your block. You might still hear these sounds to an extent, but not nearly as loudly as you did before you got the cellulose insulation installed.

Neither type of spray foam really makes much of an impact on noise. If you already live on a tranquil street, then this isn’t such a big deal. If street noise interrupts your relaxation or even keeps you from sleeping, though, then maybe it’s time to consider blown-in cellulose.

Cellulose can also be safer than spray foam, but only if yours is completely recycled. If it contains the chemical treatment borate, then it’s no safer than any other type of insulation. Spray foam can irritate those with breathing conditions such as asthma, something that happens less often with blown-in cellulose.

If you’re looking to save some money, there’s hardly a price advantage in choosing one type of insulation over the other. Blown-in cellulose might cost about $1.20 per square foot and spray foam is $1.50 a square foot. If you really want to cut down on the costs of insulation, fiberglass is a cheaper option.

Conclusion

Between spray foam and blow-in cellulose insulation, closed-cell spray foam is the better pick. It’s barely more expensive than cellulose, yet it has an R-value that’s two times higher. For Floridians especially, that higher R-value will really make a difference. You’ll be able to comfortably enjoy being in your home.

Interior view of the living room of our first net-zero renovation in Florida. Insulation was just one factor in making a quiet, comfortable, energy-efficient home.
Whatever insulation you choose, your goal is a quiet, comfortable home. We’re happy to say that’s what we achieved with our first net-zero renovation by exploring the insulation options along with the other low hanging fruit.

Since spray foam insulation can fit into narrower gaps and areas than blown-in cellulose, there’s no reason not to use both materials in different parts of your home. These forms of insulation are both low-cost enough for this to be feasible. Then you can reap all the benefits of the insulating properties of the spray foam along with the noise-reducing qualities of the spray foam. Your home will be quieter, more comfortable, and more energy efficient!

Erin Shine

Erin Shine

Founder | Attainable Home

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