Open-cell vs. closed-cell spray foam: what belongs in the proposal?

Open-cell and closed-cell spray foam have different structures and properties. The right choice depends on the assembly being insulated, available space, moisture design and the exact product specification. Neither name alone tells you whether a proposal fits your home.

Before choosing between them, confirm where the foam will be installed. A wall cavity and an attic roofline present different questions. If you are still deciding between loose fill at the attic floor and foam elsewhere, resolve that broader scope first.

The practical differences

In general, closed-cell foam is denser and provides more thermal resistance per inch than open-cell foam. The products also differ in vapor permeability. Air-barrier and vapor-control performance depend on the product and installed thickness; they should not be assumed from the word “foam.” Johns Manville’s product comparison explains these distinctions. Its examples are manufacturer-specific, not specifications for every product or a statement about the brand Time uses.

Start with the available space and required result

Ask the contractor to show the intended thickness and R-value in each assembly. If depth is limited, the product choice may affect whether the design’s thermal requirement can be achieved in that space. If two bids show the same thickness but different products, they may not offer the same thermal resistance.

The estimate should also explain how irregular areas and transitions are included. A product data sheet is useful, but it does not replace a defined installation scope.

Ask how the assembly manages moisture

Have the responsible designer or qualified professional explain how the proposed assembly handles moisture and drying. Ask which existing layers remain and whether the change affects attic ventilation, roof inspection or equipment. A product’s resistance to vapor movement does not make a leaking roof acceptable.

For a retrofit, identify conditions that need correction before application. Do not accept a material recommendation based only on “Florida weather” without an explanation of the actual building.

Compare complete proposals

• Product: exact manufacturer and product name, with current technical documentation.
• Installation: assembly, area, specified thickness and target R-value.
• Related work: preparation, removal, coverings and any design or inspection requirements.
• Occupancy: ventilation plan and product-specific instructions for returning to the building.
• Price: complete installed scope, with exclusions and options identified.

A material-price comparison alone does not tell you the cost of the completed job. Ask each bidder to explain differences in scope before deciding that one foam type is the cheaper solution.

Discuss the application with Time

Time offers spray-foam insulation for project-specific applications. When you request an estimate, describe the building, where insulation is needed and whether plans already specify a product or assembly. For a new build, include the relevant drawings so the proposal can address the intended design.