Pros and Cons of Polyiso vs EPS vs XPS for Continuous Insulation
Continuous insulation (CI) is a layer of insulation that covers the entire building envelope without any thermal bridges, such as studs, joists, or rafters. CI reduces heat loss and improves energy efficiency, comfort, and durability of buildings. CI can be applied on the exterior or interior of walls, roofs, and floors, using different types of rigid foam insulation panels. You can read more about it in our blog post on continuous insulation.
Rigid foam insulation panels are made of plastic foam that is molded or extruded into boards of various thicknesses and densities. They offer high R-values per inch, meaning they resist heat flow better than other types of insulation. They also have low moisture absorption, high compressive strength, and good dimensional stability.
However, not all rigid foam insulation panels are the same. There are three main types of rigid foam insulation panels used for CI: polyisocyanurate (polyiso), expanded polystyrene (EPS), and extruded polystyrene (XPS). Each type has its own pros and cons, depending on the application, performance, cost, and environmental impact.
In this article, we will compare the pros and cons of polyiso vs EPS vs XPS for continuous insulation, and help you choose the best option for your project.
Polyisocyanurate (Polyiso)
Polyisocyanurate (polyiso) is a thermoset plastic foam that is produced by reacting isocyanates with polyols in the presence of a catalyst and a blowing agent. Polyiso is usually faced with aluminum foil or fiberglass on both sides to enhance its thermal performance, moisture resistance, and fire resistance.
Pros of Polyiso
Polyiso has the highest R-value per inch of any rigid foam insulation panel, ranging from 5.6 to 7.0 depending on the product and temperature. This means it can provide more insulation with less thickness than other types of rigid foam insulation panels.
Polyiso is compatible with most types of cladding and roofing materials, such as metal, brick, stone, wood, vinyl, asphalt shingles, etc. It can be attached with adhesives, mechanical fasteners, or hot mopping.
Polyiso is lightweight and easy to cut and install. It can be used for both new construction and retrofit applications.
Polyiso has excellent fire resistance properties. It does not melt or drip when exposed to high heat, but rather chars and forms a protective layer. It meets the requirements of NFPA 285 fire test for wall assemblies using steel studs.
Polyiso has low environmental impact compared to other types of rigid foam insulation panels. It has zero ozone depletion potential (ODP) and very low global warming potential (GWP). It also contains recycled content and can be recycled at the end of its life cycle2.
Cons of Polyiso
Polyiso is more expensive than EPS and XPS per unit of R-value. The average cost of polyiso is about 70 cents per square foot for a 1-inch-thick panel.
Polyiso is sensitive to temperature variations. Its R-value decreases as the temperature drops below 50°F (10°C), which means it performs worse in cold climates than in warm climates4. This can affect the overall thermal performance of the building envelope. A polyiso panel with a nominal R-value of 5.6 at 75°F can have an R-value of 2.0 at 15°F. This effect is directly related to the blowing agent used in manufacture; some brands have switched blowing agents so their polyiso panels maintain their R-values at lower temperatures so it pays to read the product sheets critically.
Polyiso is not very permeable to water vapor. It has a perm rating of less than 1 for foil-faced products and less than 5 for fiberglass-faced products. This means it can trap moisture inside the wall assembly if not properly detailed with a vapor retarder or barrier.
Polyiso is not very resistant to moisture absorption. It can absorb up to 3% of its weight in water when exposed to wet conditions. This can reduce its R-value and cause mold growth and rot.
Expanded Polystyrene (EPS)
Expanded polystyrene (EPS) is a thermoplastic foam that is produced by expanding polystyrene beads with steam in a mold. EPS is usually white or gray in color and has a closed-cell structure.
Pros of EPS
EPS has a consistent R-value per inch of about 4 to 4.5 regardless of temperature or moisture conditions. This means it performs well in cold climates and does not degrade over time.
EPS is the most versatile of the three types of rigid foam insulation panels. It can be used for roof, wall, floor, below grade, and structural applications. It can also be molded into different shapes and sizes to fit various design needs.
EPS is the most economical of the three types of rigid foam insulation panels. It has the lowest cost per R-value per inch, ranging from 25 to 30 cents per square foot for a 1-inch-thick panel.
EPS is approved for ground contact and below grade applications. It can be treated to resist insects and termites. It can also withstand freeze-thaw cycles and hydrostatic pressure without losing its R-value or structural integrity.
EPS is recyclable and contains recycled content. It has zero ODP and low GWP. It also reduces energy consumption and greenhouse gas emissions by improving the energy efficiency of buildings.
Cons of EPS
EPS has the lowest R-value per inch of the three types of rigid foam insulation panels. This means it requires more thickness than polyiso or XPS to achieve the same level of insulation.
EPS is not very compatible with some types of cladding and roofing materials, such as asphalt shingles, hot mopping, or torch-down roofing. It can be damaged by high temperatures or solvents. It also requires a protective layer or coating to prevent UV degradation.
EPS is not very fire resistant. It melts and drips when exposed to high heat, which can spread the fire and create toxic fumes. It does not meet the requirements of NFPA 285 fire test for wall assemblies using steel studs.
EPS is somewhat permeable to water vapor. It has a perm rating of about 5 for a 1-inch-thick panel. This means it can allow some moisture to pass through the wall assembly if not properly detailed with a vapor retarder or barrier.
Extruded Polystyrene (XPS)
Extruded polystyrene (XPS) is a thermoplastic foam that is produced by extruding polystyrene through a die with a blowing agent. XPS is usually blue, green, or pink in color and has a smooth surface and a closed-cell structure.
Pros of XPS
XPS has a high R-value per inch of about 5 to 6 depending on the product and temperature. This means it can provide more insulation with less thickness than EPS but less than polyiso.
XPS is very resistant to moisture absorption. It can absorb less than 1% of its weight in water when exposed to wet conditions. This means it maintains its R-value and structural integrity even when wet.
XPS is very durable and strong. It has high compressive strength and dimensional stability. It can withstand high loads and impacts without cracking or deforming.
XPS is recyclable and contains recycled content. It has zero ODP and low GWP. It also reduces energy consumption and greenhouse gas emissions by improving the energy efficiency of buildings.
Cons of XPS
XPS is more expensive than EPS and polyiso per unit of R-value. The average cost of XPS is about 42 cents per square foot for a 1-inch-thick panel.
XPS is not very compatible with some types of cladding and roofing materials, such as asphalt shingles, hot mopping, or torch-down roofing. It can be damaged by high temperatures or solvents. It also requires a protective layer or coating to prevent UV degradation.
XPS is not very fire resistant. It melts and drips when exposed to high heat, which can spread the fire and create toxic fumes. It does not meet the requirements of NFPA 285 fire test for wall assemblies using steel studs.
XPS is not very permeable to water vapor. It has a perm rating of less than 1 for a 1-inch-thick panel. This means it can trap moisture inside the wall assembly if not properly detailed with a vapor retarder or barrier.
As you can see, there are pros and cons of polyiso vs EPS vs XPS for continuous insulation, depending on the application, performance, cost, and environmental impact. There is no one-size-fits-all solution for every project. You need to consider the specific requirements and conditions of your project, such as climate zone, building code, design preference, budget, etc., before choosing the best type of rigid foam insulation panel for your project.
If you need more guidance or assistance in selecting the best type of rigid foam insulation panel for your project, please contact Green Insulation Group today. We are experts in continuous insulation and we can help you achieve your energy efficiency, comfort, durability, and sustainability goals.