When considering attic insulation, spray foam is a popular choice due to its superior thermal performance and air-sealing properties. However, selecting between open-cell and closed-cell spray foam can be challenging. This guide explores the characteristics, advantages, and disadvantages of both types to help you make an informed decision.
Understanding Spray Foam Insulation
What is Spray Foam Insulation
Spray foam insulation is a chemical product created by combining isocyanate and polyol resin, which react to form a foam that expands upon application. This expansion allows the foam to fill cavities, crevices, and gaps, providing an effective air barrier and insulation layer. There are two primary types of spray foam insulation: open-cell and closed-cell.
Open-Cell Spray Foam
Characteristics
- Structure: Composed of cells that are not completely encapsulated, resulting in a softer, more flexible foam.
- Density: Typically has a density of about 0.5 pounds per cubic foot.
- R-Value: Offers an R-value (a measure of thermal resistance) of approximately 3.5 to 3.8 per inch.
- Permeability: Permits moisture vapour to pass through, allowing the building to “breathe.”
Advantages
- Expansion: Expands significantly upon application, effectively filling irregular spaces and hard-to-reach areas.
- Sound Dampening: Provides excellent soundproofing qualities due to its open-cell structure.
- Cost-Effective: Generally less expensive than closed-cell foam in terms of material costs.
Disadvantages
- Lower R-Value: Requires a thicker application to achieve the same insulation performance as closed-cell foam.The Spruce
- Moisture Absorption: Can absorb water if exposed, potentially leading to moisture-related issues if not properly managed.
- Structural Support: Does not contribute to the structural strength of the building due to its softer composition.Wikipedia
Closed-Cell Spray Foam
Characteristics
- Structure: Consists of completely encapsulated cells, forming a rigid and dense foam.
- Density: Typically has a density of about 2 pounds per cubic foot.
- R-Value: Provides a higher R-value of approximately 6 to 7 per inch.
- Impermeability: Acts as a barrier to both air and moisture, preventing water vapour transmission.
Advantages
- High R-Value: Offers superior thermal insulation, requiring less thickness compared to open-cell foam.
- Moisture Barrier: Effectively resists water and moisture infiltration, reducing the risk of mould and mildew.
- Structural Reinforcement: Adds to the structural integrity of the building due to its rigidity.
Disadvantages
- Higher Cost: More expensive than open-cell foam, both in material and installation costs.
- Less Flexibility: Its rigidity makes it less adaptable to the natural expansion and contraction of building materials.
- Potential for Trapped Moisture: If moisture enters, it can become trapped, leading to potential issues such as wood rot.
Comparing Open-Cell and Closed-Cell Foam in Attic Applications
Thermal Performance
Closed-cell foam’s higher R-value means it provides better insulation per inch than open-cell foam. This efficiency is beneficial in spaces where maximum insulation is needed without occupying much room.
Moisture Management
Open-cell foam allows moisture vapour to pass through, which can be advantageous in certain climates by enabling the building to breathe. However, in regions prone to high humidity or heavy rainfall, this permeability might lead to moisture accumulation and related problems. Closed-cell foam, being impermeable to moisture, offers a robust barrier against water infiltration, making it suitable for areas susceptible to dampness.
Structural Integrity
The rigid nature of closed-cell foam can enhance the structural strength of the roof and attic, providing additional support. In contrast, open-cell foam does not contribute to structural reinforcement due to its softer composition.
Sound Insulation
Open-cell foam excels in sound absorption, making it ideal for reducing noise transmission. Closed-cell foam, while providing some soundproofing, is less effective in this regard compared to open-cell foam.
Cost Considerations
Open-cell foam is generally more affordable than closed-cell foam. However, the required thickness to achieve desired insulation levels and the specific needs of the project can influence the overall cost-effectiveness.
Factors to Consider When Choosing Between Open-Cell and Closed-Cell Foam
- Climate: In areas with high humidity or heavy rainfall, closed-cell foam’s moisture resistance makes it a preferable choice. In drier climates, open-cell foam may suffice.
- Budget: If budget constraints are significant, open-cell foam offers a cost-effective solution, though it may require a thicker application.
- Space Constraints: In situations where space is limited, the higher R-value of closed-cell foam allows for thinner layers to achieve the same insulation performance.
- Structural Needs: If additional structural reinforcement is desired, closed-cell foam provides this benefit.
- Moisture Exposure: For areas prone to moisture exposure, closed-cell foam’s impermeability offers better protection against water ingress.
- Soundproofing Requirements: If reducing noise transmission is a priority, open-cell foam’s superior sound absorption makes it the better choice.
Potential Issues with Spray Foam Insulation
While spray foam insulation offers numerous benefits, it’s essential to be aware of potential issues:
Installation Challenges
- Open-Cell Foam: Due to its high expansion rate, open-cell foam can sometimes expand into unintended areas, potentially covering electrical components or blocking ventilation paths. Proper installation by trained professionals mitigates this risk.
- Closed-Cell Foam: Its dense and rigid composition makes it more difficult to remove or alter once cured. Any retrofitting or repair work requiring access to underlying structures can be more labor-intensive and costly.
Environmental and Health Considerations
- VOC Emissions: Both types of foam may emit volatile organic compounds (VOCs) during installation. Ensuring proper ventilation and allowing curing time is crucial. Professional installers should always wear appropriate protective gear.
- Sustainability: Some closed-cell foams contain high global warming potential (GWP) blowing agents. Newer formulations aim to reduce environmental impact, so it’s worth discussing eco-friendlier options with your installer.
Best Practices for Attic Insulation with Spray Foam
Work with Certified Installers
Engaging certified and experienced spray foam professionals ensures correct application, optimal insulation performance, and compliance with building regulations. Poorly installed foam can lead to issues like incomplete coverage, improper curing, or building code violations.
Perform a Pre-Installation Assessment
A thorough inspection of the attic helps identify issues such as existing moisture, ventilation requirements, and structural concerns. This evaluation guides the choice between open-cell and closed-cell foam.
Ensure Adequate Ventilation
Spray foam can impact attic ventilation. In unvented attic designs (often paired with spray foam), maintaining controlled airflow within the conditioned space is essential to prevent moisture buildup.
Consider Hybrid Systems
In some cases, using a combination of open-cell and closed-cell foam might offer the best results. For example, closed-cell foam on the roof deck for moisture protection, paired with open-cell in the walls for sound insulation, can optimise performance and budget.
Open Cell vs Closed Cell Foam Insulation: A Side-by-Side Comparison
| Feature | Open-Cell Foam | Closed-Cell Foam |
| R-Value (per inch) | 3.5–3.8 | 6.0–7.0 |
| Density | ~0.5 lb/ft³ | ~2 lb/ft³ |
| Moisture Permeability | Permeable | Impermeable |
| Structural Support | No | Yes |
| Sound Insulation | Excellent | Moderate |
| Cost | Lower | Higher |
| Expansion Rate | High (~100x) | Low (~30x) |
| Suitable for Moist Environments | Not ideal unless used with vapour barrier | Excellent |
| Flexibility | High (easy to trim and adjust) | Low (hard and rigid once cured) |
| Best Use Case | Interior walls, soundproofing, attics in mild climates | Roof decks, basements, attics in cold/humid climates |
Final Thoughts: Which is Better?
Choosing between open cell vs closed cell foam insulation comes down to your home’s specific needs:
- For budget-friendly, flexible, sound-insulating solutions—go with open cell foam.
- For maximum thermal performance, moisture resistance, and structural strength—opt for closed cell foam.
Whichever you choose, ensure you work with a certified spray foam contractor who understands the unique conditions of your home and attic structure. A proper installation is crucial to getting the full benefits of your insulation investment.
If you’re based in Ireland, Tamburah is a trusted name in energy-efficient and eco-friendly insulation. Known for our expertise in spray foam insulation for both residential and commercial properties, we deliver high-quality, tailored solutions that improve comfort and increase property value.
Contact us today to explore the best insulation option for your attic and start saving on energy bills while boosting your home’s thermal performance.