The difference between Polyiso, EPS & XPS Foam ...

Author: May

May. 27, 2024

The Differences Between Polyiso, EPS & XPS Foam Insulation Panels

Understanding Polyisocyanurate (PIR), Extruded Polystyrene (XPS), and Expanded Polystyrene (EPS)

When constructing or renovating a high-performance building envelope, you’re likely to choose between three main types of rigid foam panels: Polyisocyanurate (Polyiso, PIR), Extruded Polystyrene (XPS), and Expanded Polystyrene (EPS). Although all three are petroleum-based, their properties and performance levels vary.

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Before making a selection, you should clearly understand what you expect from these foam insulation panels to ensure you make the best choice. Each type has unique characteristics, performance capabilities, and ecological impacts.

Polyisocyanurate (PIR) Foam Panels

Overview

Polyiso, also known as PIR, is a thermoset plastic product typically produced as foam. It is commonly used as a rigid thermal insulation panel, often featuring an aluminum foil facing. Polyiso's thermal performance is rated at R6-6.5 per inch, but this performance deteriorates significantly in cold temperatures, below about 15°C.

Performance in Varying Conditions

While many insulation products perform better in colder conditions, Polyiso is an exception. In temperatures below -20°C, it provides considerably less thermal protection, which can lead to moisture damage due to its low permeability.

Usage in Commercial Roofing

Despite its limitations in cold climates, Polyiso is widely used in low slope, above-deck commercial roofing applications. It offers a high-strength facer and can be used with various roofing systems, including modified bitumen and built-up systems.

Conclusion

In colder climates, using Polyiso foam insulation may not be the best choice as it loses a significant portion of its thermal protection. For example, a study showed that a wall or roof assembly in Chicago using 2" Polyisocyanurate foam panels lost 30% more heat compared to the same assembly using 2" of EPS foam.

XPS (Extruded Polystyrene) Foam Panels

Overview

XPS foam panels, often known by the brand name Styrofoam, are rated at R5 per inch. Over time, they tend to off-gas, leading to a decrease in insulation performance, especially in below-grade applications. Above grade, XPS acts as a vapor retarder and can become even less permeable with increased thickness.

Real-World Performance

XPS foam has been found to retain moisture despite manufacturers' claims. This makes it less suitable for below-grade applications like basement insulation. It's better to use XPS above grade, where its insulative properties can be more effectively utilized.

Environmental Impact

Traditionally produced XPS uses hydrofluorocarbons (HFCs) as blowing agents, which are highly detrimental to the environment. However, newer versions manufactured by companies like DOW Chemicals are using more eco-friendly blowing agents.

EPS (Expanded Polystyrene) Foam Panels

Overview

EPS foam panels offer an R4 per inch rating and are more permeable to air and moisture compared to XPS. However, EPS’s higher permeability allows it to dry out quickly without retaining moisture.

Cost Efficiency

While EPS has a lower R value than XPS, it offers a higher R value per dollar, making it a cost-effective insulation choice. EPS foam consistency in performance over time also makes it a reliable option.

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Insights Into Polyisocyanurate (PIR)

Dual Layer Protection

Polyisocyanurate foam insulation panels come with a layer of foil on each side. This foil acts as an excellent vapor barrier, eliminating the need for an additional vapor barrier on the interior of a high-performance wall design.

Environmental Considerations

Polyiso’s blowing agents have a global warming potential similar to those used in EPS, making it an eco-friendlier choice in the right conditions. It’s particularly effective when kept above freezing temperatures and away from moisture.

Mineral Wool: A Non-Petroleum Alternative

Overview

Unlike petroleum-based foam products, mineral wool is made from recycled stone dust from industrial blast furnaces. It offers excellent R value, is fireproof, non-toxic, and does not off-gas harmful chemicals.

Performance and Application

Mineral wool is ideal for retrofitting insulation in basements and other moisture-prone areas. It’s also preferred for its superior soundproofing and fire resistance properties. While it’s more expensive than fiberglass, mineral wool offers easier installation and better overall performance.

Final Thoughts: Choosing the Best Insulation Panel

Our top recommendation, based on its recycled content and versatile applications, is mineral wool. For petroleum-based options, Polyiso is preferred in warmer climates, while EPS is excellent for below-grade applications. Despite its good performance, XPS’s environmental drawbacks place it last in our preference list. As XPS transitions to more eco-friendly agents, it will become a more viable option for above-grade use in green building.

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