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Spray Foam Fun

Short answer: Spray polyurethane foam is mixed on site from an isocyanate side (polymeric MDI) and a polyol blend containing catalysts, surfactants and fire retardants. Open-cell foam is blown mainly by water and expands about 150 times.

Closed-cell foam is blown mainly by HFC-type agents and expands about 35 to 50 times, so the 'more than 100 times' claim applies only to open-cell foam. Both types seal air well. Both are combustible and usually need a thermal or ignition barrier, and installers must manage isocyanate exposure.

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What should you know about Spray Foam Fun?

Quick facts. Each one stands alone and has a stable ID you can cite.

  1. Open-cell spray foam expands about 150 times; closed-cell about 35 to 50 times.

    DD-750-F01 · Write-up · Exhibit B (Two foams)

  2. Open-cell foam is blown mainly by water; closed-cell mainly by HFC-type agents.

    DD-750-F02 · Write-up · Exhibit B (Two foams)

Video transcript: Spray Foam Fun: Two Liquids That Swell Into Insulation

DID YOU KNOW? Spray foam insulation can expand to more than 100 times its original liquid volume, filling gaps and sealing buildings against unwanted air flow. It works through a chemical reaction between two liquid components, an isocyanate and a polyol, which rapidly form a lightweight plastic filled with tiny gas-filled cells. There are two main types: open-cell foam, which is softer and more flexible, and closed-cell foam, which is denser, more rigid, and more resistant to moisture vapor. NOW YOU KNOW!

Burned-in captions, read frame by frame (see transcript.md) · 26.2s Reel ·

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Spray Foam Fun: Two Liquids That Swell Into Insulation Instagram Reel · · 26.2s

The write-up

Two liquids that swell into insulation. Open-cell foam expands about 150 times; closed-cell about 35 to 50.

  1. Exhibit A

    Two sides

    SPF is sprayed as two liquids. One side is polymeric MDI, an isocyanate. The other is a blend of polyol resins, surfactants, fire retardants and catalysts. The polyol reacts with the isocyanate to make polyurethane, and the reaction gives off heat.

  2. Exhibit B

    Two foams

    The main difference between the two types is the blowing agent. Open-cell foam uses mostly water and expands about 150 times its liquid volume. Closed-cell foam uses mostly HFC-type agents and expands about 35 to 50 times.

  3. Exhibit C

    Lifts and heat

    Closed-cell foam is usually applied in layers ('lifts') of about 2 to 3 inches, or 2 inches or less for medium-density products, because the core can reach 130 to 150 °F. Lifts that are too thick can overheat, scorch or even ignite. Open-cell foam can go on to full depth, often up to 10 inches, in one pass.

  4. Exhibit D

    Air sealing and fire

    Both types are good at air sealing because the expanding liquid fills gaps and cracks. Both are combustible, so building codes typically require a thermal barrier, such as 1/2-inch gypsum board, or in some attics and crawlspaces an ignition barrier.

  5. Exhibit E

    Safety

    Installers wear respiratory protection and ventilate the work zone because of isocyanate exposure. EPA says some manufacturers recommend about 24 hours before re-occupancy, but the time varies by product.

Questions people ask about Spray Foam Fun

About how much does open-cell spray foam expand?

Open-cell expands about 150 times; closed-cell about 35 to 50 times.

Source: Write-up · Exhibit B (Two foams) · US DOE Building America: Which Spray Foam Is Right For You?

What is the main blowing agent in open-cell foam?

Open-cell foam uses mostly water; closed-cell mostly HFC-type agents.

Source: Write-up · Exhibit B (Two foams) · US DOE Building America: Which Spray Foam Is Right For You?

Which isocyanate is the A-side of most SPF?

Polymeric MDI reacts with the polyol blend.

Source: Write-up · Exhibit A (Two sides) · US DOE Building America: Which Spray Foam Is Right For You?; US EPA: Spray Polyurethane Foam Product Types (Safer Choice archive)

Why is closed-cell foam sprayed in thin lifts?

Core temperatures can reach 130 to 150 °F.

Source: Write-up · Exhibit C (Lifts and heat) · US DOE Building America: Which Spray Foam Is Right For You?; US EPA: Contractor Checklist, Safer Practices for Installing High-Pressure Two-Component SPF

What typically covers spray foam in living spaces?

Both foams are combustible, so a thermal barrier is usually required.

Source: Write-up · Exhibit D (Air sealing and fire) · US DOE Building America: Which Spray Foam Is Right For You?

Test Your Knowledge

All quizzes →

5 questions, all from this case file. Answers are revealed instantly.

  1. About how much does open-cell spray foam expand?

    1. 5 times
    2. 35 to 50 times
    3. About 150 times
    4. 1,000 times
    Show the answer

    Answer: C. About 150 times Open-cell expands about 150 times; closed-cell about 35 to 50 times. Source: Write-up · Exhibit B (Two foams) · US DOE Building America: Which Spray Foam Is Right For You?

  2. What is the main blowing agent in open-cell foam?

    1. Water
    2. Helium
    3. Propane
    4. Nitrogen
    Show the answer

    Answer: A. Water Open-cell foam uses mostly water; closed-cell mostly HFC-type agents. Source: Write-up · Exhibit B (Two foams) · US DOE Building America: Which Spray Foam Is Right For You?

  3. Which isocyanate is the A-side of most SPF?

    1. Polymeric MDI
    2. Toluene
    3. Methanol
    4. Styrene
    Show the answer

    Answer: A. Polymeric MDI Polymeric MDI reacts with the polyol blend. Source: Write-up · Exhibit A (Two sides) · US DOE Building America: Which Spray Foam Is Right For You?; US EPA: Spray Polyurethane Foam Product Types (Safer Choice archive)

  4. Why is closed-cell foam sprayed in thin lifts?

    1. To save money
    2. The reaction's heat can overheat thick layers
    3. It dries faster in the sun
    4. Code bans thick foam
    Show the answer

    Answer: B. The reaction's heat can overheat thick layers Core temperatures can reach 130 to 150 °F. Source: Write-up · Exhibit C (Lifts and heat) · US DOE Building America: Which Spray Foam Is Right For You?; US EPA: Contractor Checklist, Safer Practices for Installing High-Pressure Two-Component SPF

  5. What typically covers spray foam in living spaces?

    1. Nothing
    2. A thermal barrier such as drywall
    3. Plastic wrap
    4. Paint only
    Show the answer

    Answer: B. A thermal barrier such as drywall Both foams are combustible, so a thermal barrier is usually required. Source: Write-up · Exhibit D (Air sealing and fire) · US DOE Building America: Which Spray Foam Is Right For You?

Cite this case file

Easterling, Marcus. "Spray Foam Fun." The Detail Department (DetailEnjoyer), case file DD-750, last updated Oct 13, 2026. https://detailenjoyer.com/case/spray-foam-fun/

Permalink: https://detailenjoyer.com/case/spray-foam-fun/ · Last updated

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