Which Insulation Holds the Better R-Value Over Time: EPS or XPS?

When researching rigid insulation, it is common to encounter both EPS and XPS products. They may seem similar initially, but there are a few key differences to note that can help in determining which product is best for your specific project.

Both are closed-cell foam insulation. Both use a polystyrene base. Both provide effective insulation and are used to make buildings more energy-efficient.

The key difference is how these materials are manufactured. The process to manufacture expanded polystyrene insulation (EPS) means your final product is more consistent, more customizable and has a lower environmental impact when directly compared to extruded polystyrene insulation (XPS).

How Molded Expanded Polystyrene Is Made

While made from the same polystyrene base, EPS and XPS insulation are created using very different methods.

EPS is expanded polystyrene insulation manufactured using molds and integrated blowing agents that transform the material from a solid to a foam plastic.

Steam is used in an initial process that softens and expands the polystyrene. Then the product is transferred to a mold where steam is used a second time to further soften and expand the polymer and product into blocks or the custom shape needed.

The blocks can then be cut into any shape or size the customer wants using hot wires.

By the time EPS is sold to customers, the product is 98% air and 2% polystyrene.

How XPS Is Made

XPS is also a polystyrene product, but it is manufactured using an extrusion process.

A key difference with XPS insulation is that it is not made in a mold or contained space. Instead, it comes out as an extruder dye. In this process, the polymer is heated and mixed with a blowing agent as it goes through the extruder.

In the end, XPS insulation is a rigid foam that has a polystyrene matrix filled with a blowing agent. It has less flexibility in size and customization because of its limited extrusion options.

What You Need to Know About Insulation Value

When it comes to insulation, it is all about slowing down the heat transfer process.

Heat flows in three different ways: conduction, convection and radiation. Conduction is when heat moves through direct contact with a material, convection is heat movement through the air, and radiation is the transfer of thermal energy.

A product’s insulation value is dependent upon how it handles all three factors: it’s determined by how heat conducts, convects, and radiates through a product.

R-Value: EPS vs. XPS

The R-value, or “thermal resistance” value, is the rating used to grade how well an insulation product performs according to its conduction, convection, and radiation resistance, as discussed above.

XPS typically has a slightly higher initial R-value than EPS initially since it contains a trapped blowing agent. Over the course of time, the R-value drops because the added blowing agents found in the final product eventually is replaced with air making the product less heat resistant. An initially rated R-value 5.0 XPS product will eventually drop to closer to an R-value of 4.3.

Since EPS is made up of only air and polystyrene, its R-value does not depreciate over time. The R-value on day one, ten, twenty, even fifty years later is still the same, meaning EPS performs more consistently over the long term.

The Environmental Impact of EPS vs. XPS

When evaluating the environmental impact of various insulation products, it is important to go beyond just looking at the product’s carbon footprint. It is more reliable and accurate to look at the Environmental Product Declaration, which is a transparent, objective, and comprehensive report that tells you what a product is made of and how it impacts the environment across the product’s entire life span.

Generally, there are six categories that are common in an insulation Environmental Product Declaration. When directly comparing EPS and XPS products of the same exact density, their impacts are close in four of the six categories. There is a distinct difference between the two when global warming potential and ozone depletion potential are compared.

EPS is slightly better than XPS when it comes to global warming potential. But when looking at ozone depletion potential, EPS is significantly better than XPS and has a much lower impact on the ozone layer.

When directly compared according to Environmental Product Declaration reports, EPS proves to have less of a negative impact on the environment than XPS.