Materials explained

Open cell or closed cell? Start with the assembly.

The better choice depends on the space, moisture design and the specified product.

In this guide

Understand the distinction
Check moisture and thickness requirements
Ask for the documentation

Understand the distinction

Open-cell foam has a more open internal structure; closed-cell foam has a denser cellular structure. Closed-cell products generally provide more thermal resistance per inch. Use the actual manufacturer’s product data rather than assuming all foams perform alike.

Check moisture and thickness requirements

Vapor behavior, available cavity depth and the surrounding materials matter. A material described as moisture resistant is not a repair for a leak. Ask the designer or installer how the complete assembly manages water and drying.

Ask for the documentation

Request the product name, technical data sheet, evaluation report and applicable installation instructions. Confirm required coverings, substrate conditions and local approval. A product decision should follow the assembly design, not a blanket rule that one foam is always better.

Technical background: Natural Resources Canada — Insulation materials. Sources checked October 20, 2026. General planning information; the project professional must verify product instructions and applicable local requirements.