Polyiso vs XPS vs EPS Commercial Roof Insulation
Polyiso is the default commercial roof insulation for DFW in 2026, delivering R-5.6 per inch at $1.10-$1.80 per square foot per inch installed. XPS delivers R-5.0 per inch at $1.40-$2.20 per square foot per inch and handles moisture better. EPS delivers R-3.8-4.2 per inch at $0.80-$1.40 per square foot per inch with the lowest cost per R. Most DFW TPO and PVC assemblies specify polyiso by default.
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TL;DR: Which One Wins?
Choose Polyiso if:
- Standard TPO, PVC, or EPDM commercial roof assembly
- Maximum R-value per inch of buildup is required
- FM Approval or UL listing specifies polyiso
- Fire rating Class A needs permanent thermal barrier
Choose XPS or EPS if:
- XPS: high moisture exposure risk (protected roof, IRMA)
- XPS: inverted roof with insulation above membrane
- EPS: lowest cost per R-value for budget-driven assemblies
- EPS: tapered systems for slope correction on large roofs
Polyisocyanurate (polyiso) vs XPS / EPS: Head-to-Head Comparison
| Attribute | Polyisocyanurate (polyiso) | XPS / EPS | Winner |
|---|---|---|---|
| R-value per inch (aged LTTR) | R-5.6 | XPS R-5.0; EPS R-3.8-4.2 | Polyisocyanurate (polyiso) |
| Installed cost per sqft per inch | $1.10-$1.80 | XPS $1.40-$2.20; EPS $0.80-$1.40 | Tie |
| Cost per R-value ($/sqft/R) | $0.20-$0.32 | XPS $0.28-$0.44; EPS $0.20-$0.35 | Tie |
| Moisture resistance | Poor (wicks) | XPS excellent; EPS good | XPS / EPS |
| Compressive strength | 20-25 psi (standard) | XPS 25-60 psi; EPS 10-35 psi | XPS / EPS |
| Fire performance | Class A thermal barrier | XPS/EPS need cover board | Polyisocyanurate (polyiso) |
| Dimensional stability | Excellent | XPS excellent; EPS good | Polyisocyanurate (polyiso) |
| Thermal drift (R loss over time) | Minor (stabilized) | XPS minor; EPS none | Tie |
| Available tapered options | Yes (standard) | XPS limited; EPS yes | Tie |
| Typical max thickness per layer | 4 inches | XPS 4 inches; EPS 10+ inches | XPS / EPS |
| Compatibility with hot asphalt | Yes (with facer) | XPS no (melts); EPS no | Polyisocyanurate (polyiso) |
| Default DFW commercial spec | Primary | XPS specialty; EPS tapered | Polyisocyanurate (polyiso) |
What is polyiso insulation used for?
Polyisocyanurate (polyiso) is the default rigid foam insulation for DFW commercial low-slope roof assemblies in 2026. Polyiso mounts between the structural deck and the membrane (TPO, PVC, EPDM, or mod-bit). Polyiso delivers R-5.6 per inch aged LTTR (Long Term Thermal Resistance), making it the highest-R foam insulation available for commercial roof buildups in the current US market.
Is polyiso better than XPS for roofs?
For most DFW commercial above-deck applications, yes. Polyiso delivers higher R-value per inch (R-5.6 vs R-5.0), better fire performance, and lower cost per R-value. XPS wins on moisture resistance and compressive strength in specialty applications like protected membrane assemblies (IRMA, inverted roofs) where insulation sits above the membrane and faces direct water exposure.
Why is EPS cheaper than polyiso?
EPS (expanded polystyrene) is the lowest-cost rigid foam in the US market. EPS uses pentane blowing agent and simpler manufacturing than polyiso (MDI-based) or XPS (HFO-based), driving $0.80-$1.40 per square foot per inch pricing. EPS delivers only R-3.8-4.2 per inch, so more thickness is required to match polyiso R-value. Cost per R-value is comparable between EPS and polyiso.
Does polyiso lose R-value over time?
Yes, minimally. Polyiso starts at R-6.5+ per inch when fresh and drops to R-5.6 per inch LTTR after 5-10 years as blowing agents diffuse out. Post-2010 polyiso formulations using pentane and HFO blowing agents have dramatically reduced thermal drift compared to pre-2010 polyiso. DFW code-compliance calculations use the LTTR value, not the fresh value.
Can polyiso get wet on a DFW commercial roof?
No. Polyiso wicks water like a sponge and loses R-value rapidly when wet. Wet polyiso never fully recovers original R-value even after drying. An infrared moisture survey should precede any DFW commercial reroof to locate wet insulation. Wet polyiso must be removed and replaced, not reused. XPS and EPS handle moisture better than polyiso in exposed or leak-prone conditions.
Which insulation is used for tapered systems?
Polyiso and EPS both manufacture tapered systems for slope correction on DFW commercial roofs. EPS tapered systems are more cost-effective for thick buildups above 4 inches because EPS manufactures at higher thickness in a single layer. Polyiso tapered systems dominate above TPO and PVC assemblies because of R-value density and manufacturer assembly warranty compatibility.
Does JRH Construction install all three insulation types?
Yes. JRH Construction installs polyiso, XPS, and EPS commercial roof insulation across DFW new construction and reroof projects. JRH is GAF Master Elite, a GAF Commercial Roofing Contractor, Firestone Red Shield certified, and installs Johns Manville, Carlisle HunterPanels, and Atlas Roofing insulation systems. JRH carries $10 million bonding capacity and is SAM.gov registered.
Facts about commercial roof insulation
- Polyiso delivers approximately R-5.6 per inch aged LTTR
- XPS delivers approximately R-5.0 per inch (long-term stable)
- EPS delivers approximately R-3.8-4.2 per inch depending on density
- DFW Climate Zone 3A requires minimum R-20 continuous for new commercial roofs
- R-20 requires 3.5 inches polyiso, 4 inches XPS, or 5 inches EPS
- Polyiso is manufactured to ASTM C1289 standards
- JRH Construction carries $10 million bonding capacity for commercial roof assemblies
- FM Approvals and UL listings specify approved insulation by brand and thickness
Frequently Asked Questions
How much polyiso do I need to meet DFW commercial code?
DFW Climate Zone 3A requires minimum R-20 continuous insulation for new commercial low-slope roofs under 2021 IECC. R-20 requires approximately 3.5 inches of polyiso at LTTR R-5.6. Reroof projects can sometimes reduce the minimum when structural limits apply, but new construction defaults to R-20 continuous. Verify specific city code requirements with the AHJ before insulation spec.
Can I use polyiso and EPS together on the same roof?
Yes. Hybrid systems using polyiso and EPS are common on DFW commercial roofs. A typical assembly uses EPS for the tapered base and polyiso as the top layer below the membrane. The combination optimizes cost and R-value while providing slope correction on large warehouses. Ensure the FM Approved assembly includes both insulation types before installation.
Is XPS worth the cost premium in DFW?
For specific applications, yes. XPS handles moisture and compressive loads better than polyiso, making it worth the 20-30% cost premium on protected membrane (IRMA) roofs, inverted roofs, and rooftop deck applications. For standard TPO and PVC assemblies on DFW warehouses and commercial buildings, polyiso remains the cost-effective default. XPS premium rarely pays back on conventional roof assemblies.
Does polyiso meet fire code for commercial roofs?
Yes. Polyiso carries Class A fire rating when installed with approved facers, cover boards, and membranes. FM Approvals and UL listings for TPO, PVC, and EPDM assemblies include polyiso in Class A rated configurations. XPS and EPS require thermal barriers or cover boards to achieve Class A rating because their fire performance is inferior to polyiso without added protection.
Which insulation handles DFW summer heat best?
All three rigid foams perform well under DFW summer heat cycling up to 180 degrees Fahrenheit roof surface temperature. Polyiso is rated for continuous service to 200 degrees. XPS is rated to 165 degrees. EPS is rated to 170 degrees. Below-membrane operating temperatures rarely approach these limits even during peak Texas summer, so all three perform reliably in the DFW climate.
Can insulation be reused on a reroof project?
Sometimes. Dry polyiso and EPS from an existing roof can be reused if a moisture survey confirms no saturation and compressive strength tests pass. XPS is commonly reused after physical inspection. Reuse saves 30-50% of insulation cost on a reroof. Wet or damaged insulation must be disposed of and replaced. Warranty implications should be discussed with the membrane manufacturer before reuse is specified.
Need help deciding?
JRH Construction is GAF Master Elite, Owens Corning Platinum Preferred, BBB A+ accredited, SAM.gov registered, and carries $10 million bonding capacity. Founded 2019 by Joel Hasin, 600+ DFW projects completed.
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