As you browse building materials for your construction project, you may become overwhelmed with decision paralysis, especially when choosing between different types of insulation. The key to making the right choice is to broadly narrow down your options as far as possible, and then do a thorough comparison on the remaining few.
If that’s where you’re at—you’ve narrowed down your selection to a few options, and you’re faced with choosing between polystyrene and polyiso board insulation—we can help.
Let’s cover the basics, first.
What is Polystyrene Insulation Board?
Polystyrene is a plastic-based polymer that is used to create polystyrene foam board insulation. In its raw form, polystyrene looks like small plastic beads. The polymer beads can be manipulated with heat and blowing agents to encapsulate air and other gasses to manufacture two major types of foam insulation commonly used in construction today: extruded polystyrene (XPS) and expanded polystyrene (EPS).
Extruded Polystyrene
Extruded polystyrene is commonly called XPS, blue board, or pink board. XPS is made with polystyrene beds that are melted, compressed, and extruded into board shapes of varying sizes. Extruded polystyrene rigid insulation board is used in everyday construction; it’s often found in below-grade applications.
Expanded Polystyrene
Expanded polystyrene is called EPS, or beadboard, in construction lingo. EPS is made by using steam to expand and inflate the polystyrene pellets. The expanded pellets are then placed in molds and steam-fused together. After that, they cool and are cut to custom sizes. Expanded polystyrene board insulation is used in construction throughout the entire building envelope.
Disadvantages of Polystyrene
When comparing polystyrene to other building materials, such as polyisocyanurate board insulation, it’s important to consider weaknesses. Here’s where rigid polystyrene insulation boards fall short:
Limited Service Temperature
Polystyrene is a thermoplastic material, meaning it can become malleable and will melt above a certain temperature. Both extruded and expanded polystyrene have a maximum service temperature of about 165 degrees Fahrenheit.
Since building envelope surface temperatures commonly exceed this temperature in the summer months, that could mean disaster for polystyrene foam board insulation.
Low Melting Point
The type of building materials you choose can have a big impact on how well your structure can survive a devastating event like a fire. With its low melting point, polystyrene insulation can pose a higher risk than other building materials during a fire.
Rather than being fire-resistant or fire-retardant, polystyrene melts when exposed to flame. The liquified material can drip and spread fire to other parts of the building.
R Value
Thermal resistance, or R-value, is a key consideration when choosing your insulation.
Higher R-values mean that your insulation works better to keep temperatures stable inside your building. A higher R-value per inch means that you can achieve the same code performance level with less material. Polystyrene insulations carry an average R-value of around R4 or R5 per inch, varying slightly depending on the type and density used. This is a middle-of-the-road value and there are better insulators than polystyrene board insulation if you need a higher R-value per inch for your project.
Water Permeance and Absorption
Insulation that absorbs water can compromise the insulating value and can lead to mold and other problems over time. Expanded polystyrene insulations have water absorption of between 2-4%. Surprisingly, this is higher than other types of insulation, which can achieve less than 1% water absorption. Similarly, water vapor permeance measures whether vapor can pass through the insulation.
Expanded rigid polystyrene board insulations carry a water vapor permeance of between 2.5 to 5 perms, which allows vapor to pass through at a higher rate than extruded polystyrene or polyiso.
Polyiso Instead of Polystyrene
Now that we’ve covered some of the shortcomings that come with polystyrene board insulation, let’s introduce a better solution—polyiso.
Here’s why polyisocyanurate, or polyiso, is superior to polystyrene. The service temperature of polyiso is nearly double that of polystyrene. Polyiso can be installed in applications up to 250 degrees Fahrenheit. Additionally, polyiso does not melt at high temperatures or when exposed to flame. Instead, it chars.
Thermal performance is another area where polyiso is the clear winner when compared to polystyrene rigid insulation board. Polyiso has an R-value of R6 per inch, which is a significant metric when you need to insulate narrow spaces like wall cavities.
Finally, when it comes to water resistance, polyiso again outperforms expanded polystyrene. Water absorption of polyiso sits at less than 1% volume and water vapor permeance at less than 1.5 perms.
Find the Best Polyiso Insulation Solutions with Rmax
Choosing between rigid polystyrene insulation board and polyiso becomes easier when you have all the facts. Are you ready to make the call and specify your building’s insulation? Rmax can help you choose the best polyiso for your next project. Reach out to your local representative to get started!