What Is Spray Foam Insulation?

A plain-language guide to what spray foam is, how it works, and why it outperforms traditional insulation.

Spray foam insulation is a two-component liquid that is mixed on-site and sprayed into wall cavities, attics, crawl spaces, and other building assemblies. When the two components combine, they react and expand into a foam that both insulates and air-seals the cavity simultaneously.

How Spray Foam Is Different from Fiberglass

Traditional fiberglass insulation slows heat transfer through conduction. But heat also moves through convection, hot air moving through gaps. Fiberglass does almost nothing to stop moving air.

Spray foam stops both heat conduction AND air movement by creating a continuous, adherent barrier that fills every gap, crack, and framing penetration. This is why spray foam dramatically outperforms fiberglass in real-world Texas heat.

The Two Types: Open-Cell and Closed-Cell

  • Open-cell: softer, lower density, about R-3.5 to R-4 per inch, vapor permeable, best for attic rooflines and acoustic control
  • Closed-cell: rigid, dense, about R-6 to R-7 per inch, vapor retarder, best for metal buildings, crawl spaces, and shallow assemblies

What Spray Foam Actually Does in a Building

  • Insulates the cavity (slows heat transfer)
  • Air-seals the assembly (stops air movement through gaps)
  • Controls vapor in the assembly (especially closed-cell)
  • Reduces duct heat loss when used in conditioned attics
  • Reduces infiltration of dust, pollen, and humidity
  • Adds structural rigidity (closed-cell only)
  • Dampens airborne sound (open-cell especially)

Why DFW Homes Benefit So Much

In North Texas, the attic is often the biggest source of heat gain because HVAC ducts are located in a space that can reach 140°F on summer afternoons. When spray foam is applied to the underside of the roof deck, it converts the attic into a conditioned space, dramatically improving duct performance and whole-home comfort.

This is why spray foam tends to show the most dramatic comfort and energy improvements in hot-climate states like Texas.

Want to See What Spray Foam Can Do for Your Home?

Texas Foam Pro will evaluate your specific structure and show you exactly where spray foam will have the biggest impact.