Compressive Resistance testing is a method that provides information regarding the behavior of cellular materials under compressive loads. Both EPS and XPS have the ability, through densities, to provide a range of compressive resistant properties. 25 PSI material is the most commonly specified property and both EPS and XPS meet that specification.

Exposure of EPS to moisture resulting from such factors as periodic, internal condensation or moist soil conditions in foundation applications do not affect the mechanical strength characteristics of EPS thermal insulation board.

EPS does not suffer from the same plight as XPS in regards to “Off Gassing.” XPS has blowing agents that initial give it a higher R-value, but these gasses escape over time lowering the R-value. The off gassing of XPS is not just a one time event. This loss is a gradual escape of gasses into the surrounding environment. With the gasses goes the R-value loss of the insulation as well. The real question is how much does it go down, how fast and over what period. Long Term Thermal Performance (LTTR), is a measurement to try and quantify these losses but it does not take into account the shrinking R-value after the first 5 years. (Learn More About LTTR)

Buildings are designed and built to last 50-100 years in most cases. If LTTR only gives use a clear picture of the first 5 years of insulation performance, how does that information effect the economies of the building? Does it cost more to operate than expected? Did we over pay for a insulation that has a shrinking R-value? Are their long-term health impacts from the off gassing? (News About LTTR)

Hydro-chlorofluorocarbons (HCFCs) are listed as a Volatile Organic Compound (VOC). XPS contains HCFC, EPS does not. As a VOC, HCFCs may be involved in reactions to produce ozone, which can cause damage to plants and materials on a local scale. At a global level however, releases of HCFCs have serious environmental consequences. Although not as stable and therefore not so persistent in the atmosphere as CFCs, HBFCs or Halons, they can still end up in the higher atmosphere (stratosphere) where they can destroy the ozone layer, thus reducing the protection it offers the earth from the sun's harmful UV rays. HCFCs also contribute to Global Warming (through "the Greenhouse Effect"). Although the amounts emitted are relatively small, they have a powerful warming effect (a very high "Global Warming Potential").

Some VOCs are dangerous to human health and breathing in these compounds have not been fully studied or understood as to the effects on human health. (More About VOCs)

Which are more valuable R-value numbers - in a lab or where they are actually being used? As a starting point, published ASTM results is important for product comparison. Unfortunately, these results are under perfect lab conditions and not real world conditions. Real world variables are numerous, however independent research over long periods in real conditions should be highly favored in design considerations.
In a 15 year study that was conducted by an independent test lab, XPS and EPS was put to the test in real world conditions. EPS foam significantly outperformed XPS foam not only in its retention of its R-value but also showed superior properties in decreased water absorption.

XPS warranties 90% of its R-value. EPS warranties 100% of its R-value. These of course are under the conditions of the warranties. (see XPS Warranties) The reason for the differences is really the Off gassing and the dropping of the R-value in XPS insulation. EPS does not suffer from dropping R-value, therefore it can give the full 100%.

* Published R-Values come directly from the manufacturer’s publications. XPS R-values were used from Owens Corning and Dow. Guaranteed R-value was from XPS Manufactures publication - See Warranties.

Plymouth Foam’s EPS is proud to made in Wisconsin. Our state has one of the best educational system in the country and it shows in our workforce. We provide many local jobs and help boost our economy. (Made in Wisconsin)

Some of the XPS is made in China or other parts of the County. But Plymouth Foam is proud to say, our EPS insulation is Made in the USA.

The Global Warming Potential (GWP) was developed to allow comparisons of the global warming impacts of different gases. According to the US Environmental Protection Agency,” the larger the GWP, the more that a given gas warms the Earth compared to CO2. GWPs provide a common unit of measure, which allows analysts to add up emissions estimates of different gases.” (EPA - Green House Gas Emissions)

The chemical compound HCFCs contribute XPS having a higher GWP than EPS. Transportation accounts for 26% of gas emissions, so buying EPS locally can help reduce gasses even more. (EPS Reduces Global Warming)

During the manufacturing process, XPS and EPS provide a far different exterior surface. XPS almost has a skin, which makes bonding to that skin less desirable. EPS on the other hand has a surface that excepts bonding very well. In fact, the Insulated Concrete Forms (ICFs), Exterior Insulated Finish System (EIFS) and the Structural Insulated Panels (SIPs) industries have found EPS to have exceptional bonding capability. These building components industries prefer EPS and believe the product is far superior to XPS. The packaging industry has also found EPS exceptional for component bonding. High end packaging prefers EPS because of its physical bonding capability.

ASTM E84 is the test method for surface burning characteristics of building materials. This test covers flame spread and smoke development. Polystyrenes (XPS & EPS) have very similar characteristic when it comes to the introduction of fire. Flame spread is identical but EPS has a lower flame spread. Some would believe in simple terms that EPS is 98% air with no blowing agent. Both products do meet the IBC requirement for building products.

The building industry is requiring more customization of products. The 4’ x 8’ sheets are ok, but more and more building professional are looking for more. Basement wall heights of 9’4” as an example, wouldn’t one piece covering the 9’4” height be better. EPS is far superior in its ability to make custom sizes, shapes and thicknesses. XPS is limited to 3” - 4” thick, where EPS can be made up to 48” thick. XPS is limited to R-15, where EPS can go up to R-209.

EPS can add lamination to its products, such as reflective facer in fan-fold. Tongue and grove, ship lap, groves, channels, wire case are just a few items that be added to EPS. The possibilities are almost endless with EPS. (See More Customization of EPS)

The difference in cost between XPS and EPS can range from 20% - 40%. EPS is always less, but more importantly it less per R-value inch as well. (by the numbers) In fact, EPS is the best value in rigid insulation.

Many building profession are learning the facts and costs of EPS and are starting to Value engineer projects (Value Engineering EPS) Recently a contractor saved $1000 on a project by just switching from XPS to EPS. (See how he did it) With all these advantages, what is keeping you from using more EPS?