The two most common types of insulation for commercial roof systems are Polyisocyanurate (Polyiso) and Expanded Polystyrene (EPS). Both are available in a variety of thicknesses and can be used in multiple applications. Polyiso is used in new construction designs more than EPS, though EPS still has it’s advantages.
Here is a quick comparison:
CATEGORY | POLYISO | EPS | WINNER |
R-VALUE PER INCH: | Higher | Lower | ISO |
COST PER SHEET: | Higher | Lower | EPS |
FIRE RESISTANCE: | UL class A rating | Combustible | ISO |
MOISTURE RESISTANCE: | Lower | Higher | EPS |
EASE OF INSTALLATION (TAPERED): | More difficult | Easier | EPS |
RIGIDITY: | More rigid | Less rigid | ISO |
SYSTEM APPLICATIONS: | Multiple | Multiple | TIE |
So which is best?
While the winner may not be so clear, both insulation types have their pros and cons. When it’s time for a new roof, contact your local roofing contractor to help you determine which insulation is best for your building and performance needs.

Polyiso

EPS
This article is part of our ‘Low Slope and Commercial Materials’ Series. Learn more about:
System Types and Surface Materials
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- TPO vs EPDM
- TPO vs PVC
- Fleeceback vs. Standard Membranes for Low-Slope Roofs
- Mechanically Attached vs Fully Adhered Roofing Systems
- Black Roofs vs White Roofs
- Is a Metal Roof Right for My Commercial Property?
- Can a Commercial Roof Coating Save Me Money
- Flat Roof Coatings – What Are They and When Are They Appropriate?
- 3 Best Commercial Roofs in Wichita, KS
- What Is a Flute-fill Retrofit on a Commercial Metal Roof and When Does It Make Sense?
- Retrofit vs. Replacement: What’s the Best Option for Your Commercial Metal Roof?
- Fleeceback vs. Standard Membranes for Low-Slope Roofs
Substrate Systems
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- Polyiso Insulation vs EPS Insulation
- What Do I Need to Know About Tapered Roofing Insulation Panels?
- What Is Cover Board and When Does it Make Sense to Include in a Low-Slope Roofing System?
- DensDeck vs Fiberboard: Which Cover Board Is Best for Low Slope Roofs?
- Commercial Roof Decking Guide: Comparing Wood, Metal, & Concrete for Low-Slope Roofs