One of the most popular types of foam insulation on the market, XPS is used in many different construction applications. Knowing XPS’s strengths and weaknesses make it much clearer on when to use it versus another type of insulation. Learn more about what XPS is, how and when to use it, and when other insulation types make more sense.
What is Extruded Polystyrene (XPS)?
Extruded polystyrene is made through an extrusion process into a rigid foam board. Blowing agents are injected into a mix of molten polystyrene before being forced through an extruder. The mix of the blowing agents and injection pressure pushing the molten mix through the extrusion die results in a foam board with tight cell spacing.
Easily recognizable by its blue, green, or pink color, XPS can be found on many job sites. This type of foam board readily accepts being faced and can be sold unfaced as a semipermeable rigid insulation board.
XPS is a closed cell foam with an R-value of around 5 per inch of thickness and is very lightweight and durable. The tight cell spacing and closed cell nature of XPS make it an excellent vapor retarder due to its low permeability, especially when faced. XPS panels also provide a great deal of compression strength and dimensional stability. During the extrusion process fire retardants can be mixed in to improve fire-resistance. XPS can even be recycled.
How is XPS Installed?
XPS panels are used in a variety of different applications, and the structural characteristics of the panels make them fairly easy to install.
Cavity Insulation
For a cavity installation, XPS panels are fairly easy to work with. XPS panels can be scored and snapped or cut with a table saw to fit the size of the wall cavity. Spray foam is typically applied along the perimeter of the cavity. Instead of spray foam, XPS compatible adhesive can be applied to the face of the panel that will go against the exterior sheathing. The cut XPS panels can then be pushed into the cavity and sealed with the spray foam.
Exterior Insulation
XPS is often installed as exterior insulation as well, especially below grade. After initial framing of the wall’s structural components, XPS panels are installed directly on the exterior of the framing members. Typically, ⅜” head galvanized nails, 1” crown galvanized staples, or equivalent fasteners long enough to penetrate at least ¾” into the framing members are used to secure the insulation.
The XPS panels are secured to the framing members using a few fasteners per board. Fasteners should not be over-driven to ensure long term stability of the installation. After the panels are secured, tape is used to seal all of the insulation joints.
How Much Does XPS Cost?
XPS tends to be slightly more expensive than EPS and a bit cheaper than polyiso foam boards. While material prices can be highly volatile, XPS typically costs around $0.42 per square foot for one inch thick panels. XPS is often used in applications with tougher requirements that EPS cannot meet. Even for general insulation purposes, XPS can still be a viable alternative due to the ease of working with the material.
Best Applications for XPS
XPS is a strong and durable foam board with respectable thermal properties. This type of foam board typically works well in applications requiring higher strength and exposure to moisture. Common applications for XPS include:
Cold storage floors
Basement and below grade insulation
Under slab insulation
Flat roof insulation
Parking decks
The compressive strength of XPS and stability over time make it a great choice for underfloor insulation. For the same reasons, XPS is often selected for insulating foundation walls.
Rmax Polyiso: The Better Choice for Continuous Insulation
XPS is a great choice for insulation, and when it comes to continuous insulation applications polyiso is also the clear winner. Continuous insulation requirements are increasing and architects, designers, and specifiers must choose which type of insulation to use for their projects. Polyiso is not only a better insulator than XPS, but is also a completely different material.
Polyiso is a thermoset while XPS is a thermoplastic. The difference between these two materials can easily be seen at elevated temperatures. XPS, being a thermoplastic, softens and melts into a liquid when heated. Polyiso, however, chars and hardens.
Due to the elevated surface temperatures of exterior walls, over time XPS may not stay in place in the same way polyiso will. The elevated temperature performance coupled with the dimensional stability, moisture resistance, and superior thermal performance of polyiso make the choice easy.
For a continuous insulation material that will perform as well decades later as the day it was installed, choose Rmax polyiso! Contact our experts today to find the perfect solution for your project.