Is closed-cell worth the extra cost over open-cell?

Yes for below-grade, crawl spaces, and where moisture resistance is needed. For standard walls and attics, open-cell is more cost-effective.

Can I DIY spray foam?

Small kits exist for rim joists and small areas. Full wall and attic applications require professional equipment and training.

Does spray foam off-gas?

During and shortly after application yes. The area must be evacuated and ventilated per manufacturer specs. Once cured (24-72 hours), it is inert.

Insulation

Spray Foam

$1.50-$3.00 per board foot installed

Closed-Cell Spray Foam: Premium Insulation Performance (2026)

Prepared by Lumberama's Building Materials Team

|Last updated August 19, 2026|Sources & methodology

Closed-cell spray foam insulation is a two-component polyurethane material that expands upon application to create a rigid, high-density insulation layer. It provides the highest R-value per inch of any common insulation while simultaneously serving as an air barrier, vapor retarder, and structural reinforcement.

Key Features

R-6.5 per inch; Air barrier and vapor retarder; Adds structural rigidity; Waterproof; Highest R-value per inch available

Specifications

R-value: R-6.5 per inch. Density: 1.75-2.25 lbs/cu ft. Vapor permeance: less than 1 perm at 1.5 inches. Compressive strength: 25+ PSI.

Applications

Exterior walls; Crawl spaces; Rim joists; Roof decks; Below-grade walls

Installation Overview

Professional installation required. Surfaces must be clean and dry. Foam is sprayed in lifts of 2 inches maximum to control exothermic reaction. Requires thermal barrier covering (drywall) when exposed to occupied spaces.

Pros & Cons

Pros

✓ Highest R-value per inch; Air seals completely; Vapor retarder built in; Adds structural strength; Waterproof

Cons

✗ Most expensive insulation; Professional installation required; Off-gases during application; Difficult to remove or modify; Must be covered with thermal barrier

Top Brands

Dow

Johns Manville

Icynene

Demilec

Code Requirements

Must meet ASTM E84 for flame spread. Thermal barrier (1/2 in drywall) required over foam in occupied spaces per IRC R316. Vapor retarder properties per IRC R702.7. Maximum lift thickness per manufacturer.

Buying Tips

Get multiple quotes from certified installers. Verify they carry proper insurance. Closed-cell is overkill for many applications - consider where open-cell or rigid foam would suffice at lower cost.