Choosing the right insulation type is essential for achieving energy efficiency and long-term savings. Two common options, injection foam insulation vs spray foam insulation, are often compared for residential and commercial projects.
Though they sound similar, they perform differently depending on structure type, wall condition, and installation needs. This guide walks you through the exact differences between the two so you can make a confident and informed decision.
Read below about the performance, cost, and materials, and how they impact your property’s efficiency and comfort.
What Is Injection Foam Insulation?
Injection Foam insulation is a type of foam injected into existing walls, typically behind drywall or exterior siding. It expands slowly to fill gaps without applying pressure to the wall cavities, making it ideal for retrofit applications where you want to improve energy efficiency without gutting the walls.
Made primarily from water-based resin or polyurethane, it’s mixed on-site and pumped through small holes drilled in the wall. After curing, it forms a dense, airtight barrier against air leakage and heat loss.
Embedding this option into older homes is common due to its minimal invasiveness and ability to fill irregular cavities. It’s a key material used in injectable wall insulation projects.
What Is Spray Foam Insulation?
Spray foam insulation, in contrast, is applied as a liquid that expands rapidly when sprayed onto open surfaces. It is best suited for new constructions, attics, basements, and crawl spaces where open access is available.
There are two main types: open-cell and closed-cell. Open-cell is softer and more flexible, while closed-cell is denser and offers better moisture resistance and higher R-value. The expansion rate of spray foam can seal even the tiniest cracks, providing excellent insulation performance and air sealing in one step.
Because of its coverage and strength, it’s often preferred when structural support or vapor barriers are needed.
Key Differences Between Injection Foam and Spray Foam Insulation
Here’s a side-by-side look at injection foam and spray foam insulation:
| Feature | Injection Foam | Spray Foam |
| Best for | Existing walls | New builds/open cavities |
| Expansion Speed | Slow (to avoid wall damage) | Fast (rapid fill of open areas) |
| Air Sealing | Excellent | Superior |
| Moisture Resistance | Moderate | High (especially closed-cell) |
| Typical R-value | ~4 per inch | 3.5–7 per inch (type-dependent) |
| Structural Support | Minimal | High (closed-cell provides rigidity) |
| Installation Invasiveness | Low (small holes drilled) | High (requires open access) |
| Cost | Moderate to High | Higher (especially for closed-cell) |
Performance Comparison of Spray Foam and Injection Foam
Both materials provide strong insulation, but their application environment impacts their effectiveness.
- Due to its gentle expansion, injection foam insulation is excellent for retrofitting older homes. It improves comfort and air quality without removing drywall.
- In newer structures, spray foam insulation outperforms by offering a continuous air and vapor barrier with high R-value and durability.
When deciding between spray foam or injection foam, evaluate the condition and accessibility of the area to be insulated.
Installation Process Comparison
Installing spray foam and injection foam follows different approaches:
Injection Foam Process:
- Drill small holes in exterior/interior walls
- Mix foam and inject slowly
- Patch holes post-installation
- Cure time: 24–48 hours
Spray Foam Process:
- Apply to open surfaces via spray gun
- Foam expands instantly
- Requires PPE due to fumes
- Cure time: a few hours to a day
Injection foam is more suitable for finished spaces, while spray foam is faster for new builds or major renovations.
Spray Foam Insulation Cost vs Injection Foam Cost
When comparing spray foam insulation cost to injection foam, expect variations due to type, thickness, area size, and labor.
- Spray Foam (Open-cell): $0.50–$0.75 per board foot
- Spray Foam (Closed-cell): $1.00–$1.50 per board foot
- Injection Foam: $1.00–$1.30 per board foot
While spray foam insulation costs more upfront, it can offer better long-term value in energy savings and structural integrity, especially with closed-cell foam.
Which One Is Right for You?
Choosing between spray foam or injection foam depends on your project type:
Choose Injection Foam If:
- You are retrofitting an older home
- Walls are closed and demolition isn’t feasible
- You need to enhance wall insulation discreetly
Choose Spray Foam If:
- You’re building a new home or doing major remodeling
- Attics, crawl spaces, or basements are involved
- You need vapor control or structural support
Always factor in your local climate, budget, and insulation goals before making a decision.
R-value and Energy Efficiency
The R-value measures resistance to heat flow—higher is better. Closed-cell spray foam insulation leads here, delivering up to R-7 per inch, while injection foam insulation generally provides R-4 per inch.
Both improve air sealing, but spray foam insulation and injection foam insulation function differently. Spray foam creates a rigid seal, ideal for moisture-prone zones. Injection foam focuses on enhancing wall performance in existing structures.
Use Cases for Spray Foam and Injection Foam
- Attics: Spray foam wins for air sealing and vapor resistance
- Exterior Walls (Retrofit): Injection foam fits with minimal disruption
- Basements: Spray foam, especially closed-cell, prevents moisture
- Soundproofing: Both help, but injection foam offers softer noise absorption
Conclusion
Choosing between injection foam insulation vs spray foam insulation comes down to your specific insulation needs, construction status, and energy goals. Both offer air sealing and thermal efficiency, but one may fit your project better.
Spray foam insulation delivers superior performance in open and new structures, while injection foam insulation excels in retrofitting and finished wall insulation.
Evaluate your budget, target areas, and installation access before deciding. When applied correctly, either material can improve your comfort, energy savings, and property value. Learn more about injectable wall insulation options and insulation best practices at Weather Foam.
FAQs
What is the main difference between injection foam insulation and spray foam insulation?
The main difference lies in the application method and use case. Injection foam insulation is injected into closed wall cavities, making it ideal for retrofitting existing structures. Spray foam insulation is applied as a liquid that rapidly expands, making it better suited for open areas in new construction or major renovations.
Is injection foam insulation better for old homes than spray foam?
Yes, injection foam is often preferred for old homes because it can be installed without removing drywall. It fills irregular cavities gently without damaging walls, making it ideal for energy upgrades in finished spaces.
Which provides a higher R-value, spray foam or injection foam?
Closed-cell spray foam insulation provides a higher R-value (up to R-7 per inch) compared to injection foam (around R-4 per inch). If maximizing thermal resistance is your goal, spray foam may offer better performance.
How do I decide between spray foam or injection foam for my project?
Consider your project type. Injection foam is the practical choice for existing, closed walls. Spray foam is more effective for new construction, attics, or open framing. Also, factor in cost, access, and moisture resistance needs.
Is there a big difference in cost between spray foam insulation and injection foam insulation?
Yes, spray foam insulation, especially closed-cell, tends to cost more due to its materials and application process. However, it may offer better long-term energy savings. Injection foam is usually more cost-effective for retrofitting existing walls. For more details, see our breakdown of spray foam insulation cost.