Polystyrene insulation is widely used in modern construction due to its lightweight nature, ease of installation, and reliable insulating properties. Two of the most popular types are Extruded Polystyrene (XPS) and Expanded Polystyrene (EPS), each offering distinct advantages depending on project requirements.
This article compares XPS and EPS to help builders, architects, and developers choose the optimal insulation for their applications. By understanding differences in thermal performance, moisture resistance, strength, and cost, construction professionals can make informed decisions that maximize both performance and long-term value.
Understanding XPS and EPS
What is Extruded Polystyrene (XPS)?
XPS is produced through an extrusion process where polystyrene resin and additives are melted and shaped, creating a closed-cell structure. This gives XPS a consistent density and uniform insulating properties, making it ideal for applications requiring high compressive strength and moisture resistance.
Common Applications:
- Suitable for heavy loads
- Below-grade insulation (foundation walls, basements)
- Roofing systems
- Wall insulation
- Cold storage facilities
Key Performance Characteristics:
- High compressive strength
- High moisture resistance
- R-Value of R-5 per inch
- Strong resistance to freeze-thaw cycles
What is Expanded Polystyrene (EPS)?
EPS is manufactured by expanding small polystyrene beads with steam and molding them into blocks or sheets. This lightweight material has a closed-cell structure with small air pockets, enhancing its insulating ability. Offered at a lower price compared to other insulation types, EPS is easy to cut, handle, and install on-site.
Common Applications:
- Above-grade wall insulation
- Roofing systems
- Below-grade insulation (with proper moisture protection)
- Structural fill and Geofoam applications
Key Performance Characteristics:
- Lightweight and easy to handle
- R-Values of R-3.6 to R-5.0 per inch
- Has vapor barrier potential
Key Differences Between XPS and EPS
Long-Term Thermal Resistance (LTTR)
Long-Term Thermal Resistance (LTTR) refers to the thermal performance of insulation over time, accounting for aging and changes in material properties.
Two key standards guide its measurement:
- ASTM C1303 (Section 5.4): Measures thermal resistance at five years, closely representing the average performance over a 15-year service life.
- CAN/ULC-S770 (Section 3.3): Defines design thermal resistance as the value after five years of gas exchange with ambient air, measured or predicted under standard lab conditions.
LTTR predicts the aged R-Value of insulations that use retained blowing agents. With buildings designed for lifespans of 50 years or more, understanding the long-term insulation performance is vital for maintaining energy efficiency throughout the building’s life.
XPS vs. EPS
| Property | XPS (Extruded Polystyrene) | EPS (Expanded Polystyrene) |
|---|---|---|
| Initial R-Value per inch | R-5 | R-3.6 to R-5.0 |
| Blowing Agent | Gaseous; contributes to high initial R-Value | Air; no added blowing agent |
| Long-Term Change | R-Value decreases over time as gases dissipate | R-Value remains stable over time |
| Long-Term Performance Benefit | Initially superior but diminishes with aging | Consistently reliable over product lifespan |
While XPS offers higher initial R-Values due to its blowing agents, those gases dissipate over time, reducing performance. EPS, using only air, provides stable R-Values, ensuring dependable long-term thermal resistance. This makes EPS particularly advantageous when prioritizing lifetime insulation performance.
Moisture Resistance
XPS is often promoted for its moisture resistance due to its closed-cell structure. However, long-term research has shown that XPS may not perform as well as commonly believed.
A 15-year study conducted by the EPS Industry Alliance compared the moisture retention of XPS and EPS in below-grade conditions. Results showed that EPS retained less water than XPS when installed side by side. Retained moisture in XPS can reduce its insulating value over time, while EPS maintains more stable performance.
SilveRboard® products feature a reflective film on both faces. When sealed and taped with approved vapor-barrier tape, the rigid foam insulation forms a continuous vapor barrier, preserving insulating value even in damp conditions. In addition, perforated SilveRboard® offers high vapor permeance, improving the drying potential of wall assemblies.
Structural Strength and Density
XPS generally has a higher compressive strength (40–60 psi), making it ideal for load-bearing applications such as roofing and foundation walls. However, high-density EPS products such as HD Envirosheet® and HD SilveRboard®, provide compressive strengths comparable to XPS of up to 60 psi at a lower cost.
High-Density EPS products are suitable for demanding structural applications while maintaining cost efficiency.
Environmental Impact and Sustainability
EPS often has a lower environmental impact compared to XPS. While XPS manufacturing involves blowing agents with relatively high Global Warming Potential (GWP), EPS is composed of organic elements — carbon, hydrogen, and oxygen — and requires less energy to produce, resulting in lower emissions. Additionally, EPS is highly recyclable and can contribute to LEED® certification, supporting sustainability and energy-efficiency goals.
Cost Considerations
EPS typically offers better long-term value due to its lower initial cost and consistent insulating performance. In contrast, XPS can be 10–30% more expensive, which can significantly impact project budgets. Over time, the stable thermal performance of EPS and its lower production costs often make it a more cost-effective choice. High-density EPS products, in particular, can deliver insulating capabilities comparable to XPS, but at a reduced price.
Additionally, EPS is easy to handle and install on-site, and its much lower price per bundle or square foot makes it an attractive option for builders seeking both efficiency and affordability.
Choosing the Right Insulation
When to Use XPS
XPS has traditionally been preferred for below-grade and foundation wall applications because of its moisture resistance, as well as for high-load-bearing uses like roofing and parking decks, particularly in climates with pronounced freeze-thaw cycles. However, research shows that EPS maintains its insulating performance more effectively over time, even in damp conditions.
When to Use EPS
EPS performs well in above-grade walls, roofing, and continuous insulation applications. With proper moisture protection, it is also effective for below-grade use. Its economic and sustainable profile makes EPS a favored choice for projects prioritizing cost efficiency and environmental impact. High-Density EPS products like HD Envirosheet® and HD SilveRboard® provide comparable strength to XPS at a better value.
EPS Innovations in Construction
Modern construction is embracing new EPS technologies that enhance performance and sustainability. SilveRboard®, for instance, features a reflective facer to boost both moisture resistance and overall thermal efficiency. Similarly, Amvic™ ICF (Insulated Concrete Forms) uses EPS to form high-performance building envelopes capable of delivering superior energy efficiency and resilience in extreme conditions. Beyond building enclosures, EPS-based Geofoam is gaining popularity in infrastructure projects—its lightweight yet durable nature makes it ideal for stabilizing roadways, retaining walls, and even green roofs.
- SilveRboard® products feature a reflective facer that enhances moisture resistance and increases thermal performance.
- Amvic™ ICF (Insulated Concrete Forms) use EPS to create high-performance building envelopes with improved energy efficiency and disaster resilience.
- EPS Geofoam is widely used in infrastructure projects, offering lightweight and durable support for roadways, retaining walls, and green roofs.
Both XPS and EPS are highly effective insulation options with distinct advantages. Initially XPS provides higher compressive strength and moisture resistance, while EPS offers consistent long-term thermal performance, better moisture management, and greater sustainability.
For most construction projects, High-Density EPS products like HD Envirosheet® and HD SilveRboard® provide similar strength and moisture resistance to XPS at a more competitive price. EPS also offers environmental advantages and more stable long-term performance.
For expert advice on selecting the best insulation for your project, contact Alleguard today.