Open Cell vs Closed Cell Spray Foam - Phoenix Climate Guide 2025
Make the right choice for your Phoenix home with our comprehensive comparison guide
Open Cell Spray Foam
- ✓ R-3.5 to R-3.7 per inch
- ✓ $0.40-$0.75 per sq ft
- ✓ Excellent sound dampening
- ✓ Breathable structure
- ✓ Best for interior walls
Closed Cell Spray Foam
- ✓ R-6.0 to R-7.0 per inch
- ✓ $1.00-$1.50 per sq ft
- ✓ Superior moisture barrier
- ✓ Adds structural strength
- ✓ Best for Phoenix attics
Complete Comparison Guide
In This Guide:
- 1. Scientific Differences & Composition
- 2. R-Value Performance Analysis
- 3. Cost Analysis for Phoenix Market
- 4. Moisture Management Capabilities
- 5. Air Sealing Effectiveness
- 6. Sound Dampening Properties
- 7. Structural Strength Benefits
- 8. Phoenix-Specific Recommendations
- 9. Decision Matrix Tool
- 10. Phoenix Project Case Studies
Scientific Differences & Composition
Open Cell Structure
Open cell spray foam consists of tiny cells that are not completely closed, creating a softer, more flexible material. The cells are broken and air fills the "open" spaces inside the material.
Key Characteristics:
- • Density: 0.5 lb/ft³
- • Cell structure: 50-80% open
- • Expansion rate: 100:1
- • Water absorption: Semi-permeable
- • Texture: Soft and spongy
Closed Cell Structure
Closed cell spray foam features cells that are completely closed and packed together, filled with a gas that helps the foam expand and provides superior insulation properties.
Key Characteristics:
- • Density: 2.0 lb/ft³
- • Cell structure: 90%+ closed
- • Expansion rate: 35:1
- • Water absorption: Impermeable
- • Texture: Rigid and firm
Chemical Composition Differences
Open Cell Components:
- • Water-blown system
- • Polyol resin (Part A)
- • Isocyanate (Part B)
- • Water as blowing agent
- • Lower MDI content
Closed Cell Components:
- • HFC/HFO-blown system
- • Polyol resin (Part A)
- • Isocyanate (Part B)
- • HFC-245fa or HFO blowing agents
- • Higher MDI content
R-Value Performance Analysis
| Thickness | Open Cell R-Value | Closed Cell R-Value | Phoenix Code Minimum |
|---|---|---|---|
| 1 inch | R-3.6 | R-6.5 | - |
| 2 inches | R-7.2 | R-13 | Walls: R-13 |
| 3 inches | R-10.8 | R-19.5 | - |
| 4 inches | R-14.4 | R-26 | - |
| 5 inches | R-18 | R-32.5 | - |
| 6 inches | R-21.6 | R-39 | Attic: R-38 |
Phoenix Climate R-Value Reality
In Phoenix's extreme heat, actual R-value performance differs from laboratory ratings:
- • Attic temperatures reaching 160°F reduce effective R-values by 15-20%
- • Closed cell maintains 90% of rated R-value in extreme heat
- • Open cell maintains 85% of rated R-value in extreme heat
- • Air sealing contributes 30-40% of total energy savings beyond R-value
Open Cell R-Value Benefits
- ✓ Cost-effective R-value per dollar
- ✓ Fills cavities completely
- ✓ No thermal drift over time
- ✓ Adequate for interior applications
Closed Cell R-Value Benefits
- ✓ Highest R-value per inch available
- ✓ Meets code with less thickness
- ✓ Maintains performance in moisture
- ✓ Ideal for space-constrained areas
Cost Analysis for Phoenix Market
| Project Type | Open Cell Cost | Closed Cell Cost | Cost Difference |
|---|---|---|---|
| 1,500 sq ft Attic (R-38) | $2,100-$2,850 | $3,750-$4,500 | +$1,650-$1,650 |
| 2,000 sq ft Walls | $1,600-$3,000 | $4,000-$6,000 | +$2,400-$3,000 |
| 800 sq ft Crawl Space | $640-$1,200 | $1,600-$2,400 | +$960-$1,200 |
| 500 sq ft Garage Ceiling | $400-$750 | $1,000-$1,500 | +$600-$750 |
Material Costs (2025)
Open Cell:
- • $0.20-$0.35 per board foot
- • Coverage: 12 board feet/sq ft @ R-38
Closed Cell:
- • $0.45-$0.65 per board foot
- • Coverage: 6 board feet/sq ft @ R-38
Labor Costs Phoenix
Open Cell:
- • $0.20-$0.40 per sq ft
- • Faster application
Closed Cell:
- • $0.55-$0.85 per sq ft
- • Multiple passes required
Hidden Cost Factors
- • Prep work: Same for both
- • Overspray protection: Same
- • Closed cell may need less framing modification
- • Open cell may need vapor barriers
ROI Comparison for Phoenix Homes
Open Cell ROI Timeline:
- • Average payback: 4-6 years
- • Annual savings: $400-600
- • 20-year ROI: 280-350%
Closed Cell ROI Timeline:
- • Average payback: 6-8 years
- • Annual savings: $500-750
- • 20-year ROI: 250-320%
Moisture Management Capabilities
Open Cell Moisture Properties
Permeability: 10-20 perms @ 3.5"
Open cell is semi-permeable, allowing moisture vapor to pass through slowly. This can be beneficial for:
- • Interior wall applications
- • Allowing walls to "breathe"
- • Detecting roof leaks early
- • Reducing condensation in some climates
Phoenix Consideration:
During monsoon season (July-September), open cell may absorb ambient moisture if not properly protected.
Closed Cell Moisture Properties
Permeability: <1 perm @ 2"
Closed cell acts as a complete moisture barrier, preventing water and vapor transmission:
- • Ideal for crawl spaces
- • Flood-resistant applications
- • Exterior wall assemblies
- • Below-grade installations
Phoenix Advantage:
Provides complete protection against monsoon moisture infiltration and dust storms.
Monsoon Season Performance Comparison
Open Cell During Monsoons:
- • May absorb up to 5% moisture by weight
- • Requires vapor barriers in high-humidity areas
- • Dries quickly when humidity drops
- • Best with proper ventilation
Closed Cell During Monsoons:
- • Zero moisture absorption
- • Acts as built-in vapor barrier
- • Prevents mold growth substrate
- • Maintains R-value in all conditions
Air Sealing Effectiveness
Both open and closed cell spray foam provide excellent air sealing, but with different characteristics:
| Air Sealing Metric | Open Cell | Closed Cell |
|---|---|---|
| Air Permeability @ 3.5" | <0.02 L/s-m² @ 75 Pa | <0.02 L/s-m² @ 75 Pa |
| Typical ACH50 Reduction | 50-70% | 60-80% |
| Gap Filling Ability | Excellent (100:1 expansion) | Good (35:1 expansion) |
| Minimum Thickness for Air Barrier | 3.5 inches | 1.5 inches |
Phoenix Dust Storm Protection
In Phoenix's frequent dust storms (haboobs), air sealing is critical:
- • Both foams seal gaps down to 1/16" effectively
- • Closed cell provides secondary defense with moisture barrier
- • Open cell's expansion fills irregular cavities better
- • Either option reduces dust infiltration by 95%+
Sound Dampening Properties
Open Cell Acoustic Performance
STC Rating: 37-39 @ 3.5"
NRC: 0.70-0.75
Open cell's soft, spongy structure excels at absorbing sound waves:
- ✓ Reduces airborne noise by 50-60%
- ✓ Excellent for media rooms
- ✓ Great between floors
- ✓ Dampens high-frequency sounds
Closed Cell Acoustic Performance
STC Rating: 35-37 @ 2"
NRC: 0.50-0.55
Closed cell's rigid structure provides moderate sound reduction:
- ✓ Reduces airborne noise by 35-45%
- ✓ Better for impact noise
- ✓ Structural vibration dampening
- ✓ Low-frequency reduction
Phoenix Airport Noise Considerations
For homes near Sky Harbor or flight paths:
- • Open cell recommended for interior walls and ceilings
- • Closed cell for exterior walls with open cell interior layer
- • Combination achieves STC 45+ ratings
Structural Strength Benefits
| Structural Property | Open Cell | Closed Cell |
|---|---|---|
| Compressive Strength | 4-8 psi | 15-25 psi |
| Tensile Strength | 10-15 psi | 20-30 psi |
| Racking Strength Addition | Minimal | Up to 300% |
| Wind Uplift Resistance | Low contribution | Significant improvement |
Open Cell Structural Notes
- • Fills cavities without adding stress
- • Flexible, accommodates building movement
- • No structural enhancement claims
- • Safe for all framing types
Closed Cell Structural Benefits
- • Adds shear strength to walls
- • Reinforces against wind loads
- • Can allow reduced framing in some cases
- • FEMA approved for flood resistance
Phoenix-Specific Recommendations
Best Applications by Location
Recommended: Closed Cell
- Phoenix Attics: Handles 160°F+ temperatures, moisture barrier for monsoons
- Crawl Spaces: Complete moisture protection, pest deterrent
- Flat/Low-Slope Roofs: Additional protection against pooling water
- Exterior Walls: Maximum R-value in 2x4 construction
- Garages: Chemical resistance, structural strength
Recommended: Open Cell
- Interior Walls: Sound dampening between rooms
- Cathedral Ceilings: Cost-effective R-value achievement
- Finished Basements: Allows moisture detection
- Media Rooms: Superior acoustic performance
- Budget Projects: Maximum coverage per dollar
Climate-Specific Factors
Summer Highs
Closed cell maintains performance in extreme heat
Annual Rainfall
Low moisture allows open cell in many applications
Daily Temp Swings
Both foams handle expansion/contraction well
Hybrid Approach for Maximum Performance
Many Phoenix homes benefit from using both types strategically:
- • Flash and Batt: 2" closed cell + open cell fill = moisture protection + cost savings
- • Attic/Wall Combo: Closed cell in attic, open cell in walls
- • Zoned Approach: Closed cell in problem areas, open cell elsewhere
- • Budget Optimization: Closed cell where critical, open cell for bulk insulation
Decision Matrix Tool
Quick Decision Guide
If your primary concern is...
Choose Open Cell if:
- ✓ Budget is primary concern
- ✓ Sound dampening is important
- ✓ Interior application only
- ✓ Have adequate space for thickness
- ✓ Want to detect potential leaks
Choose Closed Cell if:
- ✓ Maximum R-value needed
- ✓ Moisture protection critical
- ✓ Limited space available
- ✓ Structural strength desired
- ✓ Exterior application
Application-Specific Recommendations:
Phoenix Attic (160°F):
→ Closed Cell
Interior Walls:
→ Open Cell
Crawl Space:
→ Closed Cell
Garage Ceiling:
→ Either (depends on budget)
Phoenix Project Case Studies
Case Study 1: Scottsdale Luxury Home
Challenge:
4,500 sq ft home with $600+ summer electric bills, multiple comfort issues
Solution:
- • Closed cell in attic (R-38)
- • Open cell in interior walls
- • Total investment: $12,500
Results:
- • 58% reduction in cooling costs
- • Eliminated hot/cold spots
- • ROI achieved in 4.2 years
- • Added benefit: 70% noise reduction
Case Study 2: Mesa Tract Home Retrofit
Challenge:
1,800 sq ft 1970s home, limited budget, poor existing insulation
Solution:
- • Open cell throughout (budget-friendly)
- • 5.5" in attic for R-20
- • Total investment: $3,800
Results:
- • 42% reduction in energy use
- • Qualified for APS rebate
- • Payback period: 3.5 years
- • Improved indoor air quality
Case Study 3: Phoenix Commercial Building
Challenge:
10,000 sq ft warehouse conversion, metal building, extreme heat gain
Solution:
- • Closed cell on metal roof deck
- • 3" application for R-19.5
- • Added white coating over foam
Results:
- • 65% reduction in HVAC runtime
- • Interior temp dropped 18°F
- • Eliminated condensation issues
- • Structural enhancement bonus
Common Misconceptions Debunked
Myth: "Open cell absorbs water like a sponge"
Reality: Open cell is water-resistant, not waterproof. It can absorb moisture vapor but drains and dries quickly. Proper installation prevents issues.
Myth: "Closed cell is always better"
Reality: Each has optimal applications. Open cell often provides better value for interior applications and sound control.
Myth: "Spray foam causes roof damage"
Reality: Properly installed spray foam actually protects roofs by eliminating moisture and maintaining consistent temperatures.
Myth: "You can't combine both types"
Reality: Hybrid applications often provide the best performance and value, using each type's strengths strategically.
Frequently Asked Questions - Phoenix Climate
Q: Which is better for Phoenix's extreme heat - open or closed cell?
A: Closed cell performs better in extreme heat, especially in attics reaching 160°F. Its higher R-value and moisture barrier properties make it ideal for Phoenix's harsh summer conditions. However, open cell can work well for interior applications where extreme heat isn't a factor.
Q: How do monsoons affect open cell vs closed cell performance?
A: Closed cell provides complete moisture protection during monsoon season, while open cell may absorb some ambient moisture. However, Phoenix's typically low humidity means open cell dries quickly once monsoons pass. For crawl spaces and exterior applications, closed cell is recommended.
Q: What's the real cost difference for a typical Phoenix home?
A: For a 2,000 sq ft Phoenix home, open cell typically costs $3,000-4,500 for complete attic coverage, while closed cell runs $6,000-9,000. The higher upfront cost of closed cell often pays back through greater energy savings and longevity.
Q: Can I use open cell in my Phoenix attic?
A: While possible, it's not recommended for optimal performance. Phoenix attics require maximum R-value and moisture protection due to extreme temperatures. Open cell would need to be much thicker (10-12") to achieve the same performance as 5-6" of closed cell.
Q: Which type qualifies for APS and SRP rebates?
A: Both types qualify for utility rebates when professionally installed to meet R-value requirements. The key is achieving the minimum R-values: R-38 for attics and R-13 for walls. Closed cell reaches these values with less thickness.
Ready to Choose the Right Spray Foam for Your Phoenix Home?
Our experts will assess your specific needs and recommend the optimal solution
BBB A+ Rated • 2025 Torch Awards Finalist • Licensed ROC #335896