Open Cell vs Closed Cell Spray Foam: The Real Differences, Costs, and Best Uses

Spray foam insulation is one of the most effective ways to improve a building’s energy performance and air sealing. But choosing between open-cell and closed-cell spray foam depends on the structure, moisture conditions, and performance goals of the project. Understanding how each type works helps contractors and homeowners select the right material for the right location.

How Spray Foam Works

Spray foam is applied as a liquid that expands into a solid insulating layer. As it expands, it fills cracks, framing gaps, and surface irregularities, helping the home retain heat during colder seasons and reject heat during warmer months. This expansion also reduces uncontrolled air movement, which helps the heating and cooling system operate more efficiently.

There are two main types of spray foam insulation: open-cell and closed-cell.

Open Cell Spray Foam

Open-cell foam expands aggressively when applied, forming a lighter, softer insulation with interconnected cells. This allows it to fill complex framing cavities and irregular surfaces extremely well.

Open-cell spray foam is commonly used for:

• attic rooflines and underside of decking• interior wall cavities• sound reduction between rooms• large cavity air sealing

Because open-cell foam expands more, it can cover large areas efficiently and is often the more economical spray foam option for interior applications where moisture resistance is not the primary concern.

Its flexibility also allows buildings to shift slightly without cracking the insulation layer.

Closed Cell Spray Foam

Closed-cell foam expands less but cures into a dense, rigid insulation with tightly packed cells. This dense structure provides a higher insulation value per inch and greater resistance to moisture movement.

Closed-cell spray foam is often selected for:

• exterior wall assemblies• crawl spaces and basements• metal buildings and commercial structures• areas exposed to humidity or potential water vapor• projects needing higher R-value in limited space

Because of its density, closed-cell foam also adds structural reinforcement to surfaces and provides strong adhesion.

Open Cell vs Closed Cell: Quick Comparison

Open Cell Spray Foam• lighter and flexible• expands significantly when applied• typically lower material cost• excellent for interior air sealing and sound control

Closed Cell Spray Foam• dense and rigid• higher insulation value per inch• stronger moisture resistance• ideal for exterior or high-demand environments

Cost Differences Between Open and Closed Cell Foam

Open-cell spray foam generally costs less per board foot because it uses lower density material and expands more.

Closed-cell spray foam costs more per board foot due to its higher density, stronger structure, and greater insulation value per inch.

The right choice should be based on performance needs rather than price alone, since using the wrong foam type in the wrong environment can reduce long-term efficiency.

Which Spray Foam Should You Choose?

Many buildings use both open-cell and closed-cell foam in different areas to achieve the best overall performance. Interior attic assemblies may benefit from open-cell expansion, while exterior surfaces or moisture-prone locations may require closed-cell protection.

A proper evaluation of the building structure, moisture exposure, framing depth, and insulation goals will determine the correct foam selection.