What is Spray Foam Insulation and Why Use It?

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Discover what is spray foam insulation, as it has become an increasingly popular choice for insulating homes and commercial buildings. Unlike traditional fibreglass batts and blown-in insulation, spray foam insulation expands and adheres to fill every nook and cranny. When properly installed, it provides superior thermal performance and air sealing compared to other types of insulation.

How Does Spray Foam Insulation Work?

Spray foam insulation is installed using pressurized equipment, a long hose, and a spray gun applicator. As the foam components are sprayed into place, chemical reactions cause the foam to rapidly expand, adhering and conforming to all surfaces. It quickly cures into a rigid, airtight, and seamless insulation layer.

There are two main types of spray foam insulation:

Open Cell Foam

Open cell spray foam has a spongy texture with tiny air bubbles throughout. It expands 100-fold during installation to insulate and reduce air leakage.

Closed Cell Foam

Closed cell foam has a denser, more rigid structure containing trapped gasses that provide the insulation properties. It expands less and has a higher R-value per inch than open cell.

Both types of sprayed-in foam insulation start out as liquid components, expand with air to cure in under a minute, and remain in place as pliable foam.

Benefits of Spray Foam Insulation

There are many advantages to using spray foam:

  • Superior air sealing – Foam insulation expands and adheres to surfaces to fill gaps that allow air leakage.
  • Higher R-values – Spray foams provide an insulation value of R-3.5 to R-6.5 per inch.
  • Moisture resistance – Closed cell spray foam resists absorbing water.
  • Noise reduction – Dense spray foam dampens sound transmission.
  • Mold prevention – Airtight foam prevents condensation that allows mold growth.
  • Durability – Cured foam is rigid and withstands typical temperature and humidity fluctuations.
  • Versatility – Foam easily adheres to odd shapes and around obstructions.

Uses for Spray Foam Insulation

Here are some of the most common and suitable uses for spray foam insulation:

  • Insulating attics by spraying rafters, eaves, and kneewalls
  • Sealing rim joists and sill plate gaps
  • Insulating basement foundations and concrete walls
  • Encapsulating crawl space dirt floors before adding a vapor barrier
  • Filling wall cavities in existing finished homes without remodeling
  • Insulating HVAC ductwork runs to prevent condensation and air leaks
  • Insulating buildings with unique architecture, angles, or irregular framing

Open Cell vs Closed Cell Foam

There are a few differences between open and closed cell spray foam:

  • Open cell foam is better for acoustical insulation and interior use above ground.
  • Closed cell foam has a higher R-value per inch and superior moisture resistance for exterior use.
  • Open cell foam is more water vapor permeable while closed cell foam acts as an air and vapor barrier.
  • Closed cell foam is more rigid and better for high-temperature attic environments.
  • Open cell foam is less expensive per square foot to install.

Professional Spray Foam Installation

While spray foam insulation kits are sold for DIY use, hiring a professional insulation contractor is highly recommended for the following reasons:

  • Insufficient thickness or irregular spraying can result in poor insulation performance and voids.
  • Improper chemical mixing and nozzle technique can lead to poor expansion or cured foam results.
  • Over-expansion can damage surfaces, framing, or rafters.
  • Professionals have the experience to determine optimal foam thickness and recognize potential obstructions.
  • Contractors have the specialized equipment, compressor sizes, and PPE to spray large areas safely.

Professional installation ensures your foam insulation investment provides maximum thermal performance and air sealing results.


Spray foam insulation provides superior insulation compared to traditional materials like fiberglass and cellulose. Foam’s air sealing properties, high R-value, and versatility make it an excellent choice for attics, walls, unique architectural features, and critical junctures prone to air leakage. While DIY spray foam kits are available, hiring professional spray foam insulation contractors is recommended to ensure proper installation and performance.

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