What you should know about EPS and XPS rigid board insulation products

What you should know about EPS and XPS rigid board insulation products.

 Rigid board insulation is an insulation that comes in the form of a board.  These can be installed internally and externally to enhance thermal-insulation and can also soundproof a room.  

 One of the many advantages for the rigid board insulation is that it comes in a wide variety of presentations and it has several options so you can install them throughout your construction and have it fit perfectly.

 Here are some tidbits of information that will help you make the right choice and match your construction needs with the right rigid board insulation option.

What is Rigid Board Insulation?

Rigid board insulation or rigid panel insulation are basically the same thing.  This insulation is what you commonly see in new buildings under construction as exposed exterior insulation.

They are generally made from two types of materials.

  • Foam plastics:  polyurethane, polyisocyanurate, and polystyrene.
  • Fibrous materials (bulk materials of individual fibers): rock, slag, wool, and the well-known fiberglass.

One of the well-liked characteristics for rigid board insulation is the high R-Value that results from the raw materials that are used in the manufacturing of the rigid board insulation itself.  Since they are more effective in keeping outside air outside the proper inside temperature steady, they are more expensive than other alternatives.

In addition, it is important that rigid board insulation boards are protected from UV rays, thus they need to be kept out of the sunlight and when they are placed they must be completely covered, otherwise, they will lose their efficiency.


EPS and XPS Rigid Board Insulation  

POLYISO (Polyisocyanurate, PIR)

The raw material for the Polyiso-based rigid board insulation is polyisocyanurate.  A characteristic of this rigid board insulation are the two faces on each side; made from both organic and inorganic material.   Depending on the manufacturing company, they might include an aluminum foil facing. 

Polyiso based rigid board insulation provides several benefits that in the long run will provide you with years of efficient insulation, energy-saving, proper weather resistance, and money-saving.  Among the most important characteristics for the Polyiso based insulation you have:

  • Thermal Efficiency
  • Dimensional stability
  • Fire resistance
  • Environmental safety

This rigid board insulation is highly versatile, so it can be of use both in residential buildings and residential construction.  However, it is recommended to use it in new constructions rather than renovations. If you plan to use it in your renovation, it might require the entire area to be used to be stripped to the core.

The best way to ensure that this is the right insulation for your project is to approach your contractor or your insulation specialist. 


EPS (Expanded Polystyrene)

One of the most commonly known materials for rigid board insulation is the EPS or “beadboard”.  EPS stands for “expanded polystyrene” which is the material from which comprehended coffee cups and other disposable picnic products in the last century.

EPS has been around humankind since the 1950s.  The EPS comes in small beads which are then expanded with air and molded in different shapes.  Here, the chosen shape is a board. This results in a lightweight, compact and efficient rigid board insulation product.

There are some misconceptions about a few benefits and characteristics of the EPS rigid board insulation and any insulation that uses EPS as the raw material. 

While EPS provides:

  • High thermal insulation
  • Water repellent
  • Dust repellent
  • High stability
  • Economical

There are some misconceptions about EPS, the most important one refers to the idea that EPS is either fireproof or fire retardant.  EPS is neither. EPS succumb to fire, though it is not a fire hazard. 

For EPS to melt it needs to be exposed to high temperatures for an extended period.  As with any other material, a brief exposure to direct fire will cause scorching; but it will not cause the material to “catch fire” immediately. 

The longer the exposure to fire, the highly likely that the material will succumb and meltdown.  However, there are more risks if this were to happen, such as toxic fumes and byproducts.

It is a very good insulation material provided that you keep the integrity of the area and make sure that electrical accidents and fires are not to happen in your building or construction. 

In addition, and while EPS is water repellent, the material itself is not sealed and there are small crevices that can hold up to 1.5 drops of water which can result not in mold nor mildew but in humidity stench. 

Once the humidity stench settles in the EPS, it can be removed but it will take time and money.

XPS (Extruded Polystyrene)

XPS comes from the same original material than EPS.  The difference between the two lies in their resistance to moisture.  I have mentioned that EPS can hold a few droplets of water and that this could very well lead to humidity smell.

XPS is of common use for below-grade waterproofing and roof systems where the insulation is placed over the membrane of the roof.  This concept is not only applied to roofs but also to walls where there is a need to place insulation over the barrier membrane. 

Yet, and just like with EPS there is the misconception that this material is also fireproofed and/or fire retardant and this is neither true.  XPS comes from the same material as EPS and therefore it reacts in the same way to fire exposure.

This is important information depending on the location and way in which the rigid board insulation will be installed in your construction.  It is also important information if you are planning on renewing an existing construction.

Both rigid board insulation products are energy efficient and have strong R-values; even though the numbers and efficient rate for the XPS is higher than EPS. 

Sadly, neither are highly versatile, nor stand in their efficiency for a long period and finally, neither are environmentally friendly. 

If you are seeking for something that is environmentally friendly, neither EPS nor XPS should be your choices. 

EPS insulation

 These are the general and more commonly used materials to manufacture rigid board insulation.  However, there are more alternative and as technology advances and new engineers appear in the construction world, there are bound to be more alternatives and new and more efficient materials and products.

It would be no surprise to see a rigid board insulation product that has all the benefits and none of the disadvantages plus being 100% environmentally friendly and recyclable.

At the moment, the choices are limited even though there are many alternatives for the construction specialist and the homeowner who wants to have the best for their money’s worth AND be environmentally responsible. 

Still, there are alternatives and good rigid board insulation products from the most popular and best quality brands in the area.


 One of the most popular rigid board insulation products available in the market, Foamular 150, comes from the well-established insulation manufacturer Owens Corning.

 Foamular 150 raw material is XPS, which, as has been mentioned, it is also  Polystyrene. However, and unlike with some competitors where the XPS rigid board insulation can hold a droplet of water, the Foamular 150 from Owens Corning cannot as there are no small spaces between the extruded polystyrene beads.

 In addition, Foamular 150 can resist water to a point where you can even say that is water repellent!  Since it is a closed cell, there is no humidity stench that you need to worry about.

 It is one of the most versatile ones in the market so much so you can use the Foamular 150 in both residential and commercial constructions in wall furring, cavity walls, crawl spaces and sheathing to name just a few.  Your imagination and the imagination of your constructor are the limit!

 To ensure that the water resistance feature works perfectly, it is important for whoever will instal Foamular 150 to seal all the joints in a proper and efficient way. 

 Doing so will not only ensure proper functioning regarding water resistance but also will ensure that the fire retardant aspect of the Foamular 150 works adequately.

 And despite all the benefits and the–almost- incredible versatility for the Foamular; this is not a rigid board insulation that you should lie on the basement and leave exposed.

 Like any other rigid board insulation, the Foamular should be fully covered and never exposed. There are areas where the Foamular can be installed only with the covering of a thermal barrier.  For more information, contact your Owens Corning specialist.

RMAX R-Matte Plus

 From Rmax comes this alternative for those constructors and renewing specialists that seek for a different approach to rigid board insulation.  R-Matte Plus-3 has a durable white-matte reinforced aluminum facer that is non-glare. 

 The Rmax R.matte plus has been designed to be used specifically in cavity walls, masonry walls and vaulted ceilings though it is not its only use.  The versatility that has been one of the best characteristics of the Rmax products allows the R-matte plus to be used in a wide variety of other locations.

 One of the most common alternatives is building envelope continuous insulation for new buildings.  It is SO user friendly and easy to install that it is also an excellent choice for Sunday do-it-yourselves.

Besides all the advantages that the Rmax R-matte plus has to offer the homeowner or the building contractor, it is important to mention that the price of this rigid board insulation product is highly competitive, thus enhancing the appeal in terms of overall cost.

 It is important to mention as well that the Rmax R-matte plus is also moisture resistant and vapor resistant, which makes it perfect for attic insulation.  As with many other polystyrene products, the R-matte plus is also lightweight. 

Rigid board insulation

 Common Uses for Rigid Board Insulation

 Rigid board insulation is a highly versatile form of insulation whose secondary strongest characteristic is that it is light.

 At the beginning of this article, I mentioned that there are other base materials for rigid board insulation boards.  Those other materials have their own different R values. Limiting ourselves to the specific raw material of this article:  Polystyrene, this belongs to a generality of raw materials where foam has a higher R value than fiberglass, cotton or cellulose.

 This means that their performance is far better than what would be anticipated otherwise.  It is important to remember that despite the compressive strength, permeability to vapor, resistance to water itself, weight and even cost; all foam based rigid boards, raw materials come from oil.  Crude oil.

 They are not fireproofed; they will succumb to fire even if they are fire retardant or even if they have been built to withstand fire for an extended period.  Whether these rigid board insulation products produce toxic fumes when burning or not is a debatable thing. The best way is to make sure you are installing them properly and according to the manufacturer’s specifications.

 But where can you use rigid board insulation products?  The answer is that these products are so versatile that they can be installed almost anywhere.

Rigid boards are often found on the exterior side of walls; its purpose is to provide thermal insulation in a building envelope. We find them on exterior foundation walls, and often between the foundation and the roof.

Rigid boards are also suitable for installation on the exterior of studs in a framed wall or a mass wall assembly.

Products such as EPS are usually the best choice for ground contact. They can be installed against footings or back-filled foundation walls on the exterior.

Rigid board uses

For its rigid feature, rigid boards are also great for installing between sheathing and siding.

Note that these can be installed on interior walls also and are great for compact and limited spaces because of its high R-values and dense material. In the interior walls, prior to finishing, they can be seen in shapes like batts or as pre-cut pieces.

The best way to know for sure that the rigid board insulation product that you are looking to acquire will fit adequately to your needs is to consult your insulation specialist or discuss it with your construction/renovating contractor.

There definitely IS a rigid board insulation product out there to match and cover your needs.