Rigid Insulation

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When using rigid Insulation in residential and commercial properties the most common boards used would be Polyiso (polyisocyanurate), EPS or XPS. Each type of insulation board are very different and carry different r-values and compressive strength. So lets delve into the differences of each.


Polyiso is short for Polyisocyanurate and can also be called PIR for an even shorter version. Polyiso would be one of the best performing insulation rigid foam boards on the market today giving the highest r-values for the least thickness.

Polyiso insulation can be used in so many different locations and effectively can totally replace glasswool and mineral wool in almost every application. The most common places you will find Polyiso insulation would be stud walls, floors, cavity walls, roof spaces / attics and external walls. However we are seeing in the market today a rapid growth in popularity with Polyiso in the flat roofing sector on commercial buildings. Special cloth faced or glass tissue faced Polyiso is being used on high rise buildings when replacing the older asbestos roofing materials that were used in the 80’s. Polyiso boards are the architects products of choice for this application. The reason being is first of all the insulation does not absorb moisture, it is strong and its high r-values per inch is currently in todays market best in class for the applications in which it is used.

Polyiso insulation can also be used whereby air tightness is required. Taping the joints and sealing the edges along with using airtight membranes will create an airtight home while maintaining a AAA rating for your homes insulation values.

If you wish to install this insulation in your stud walls it is easily cut with a box knife of a carpenter's handsaw. If you are using a handsaw it is a good idea if possible to cut the foil face on the insulation before you start to cut the insulation. This is not a necessity rather more of good practice as it will give you a much cleaner edge when you're done cutting. Make sure when measuring the openings in which the insulation will be getting installed into to allow for about 2-3mm  or ¼ “ wider than required so you get a nice snug fit. The tighter the fit the less chance you have of air leakage and small gaps can be worse than big holes as small gaps can cause a rushing of air effect.This method of installation is also used when working on attic floors, crawlspaces, basements and external walls.


EPS insulation would be one of the least efficient rigid board insulations today. However all is not lost as EPS has a high compressive strength and is great for carparks or floors that are carrying a little more weight than usual. Also EPS insulation would be widely used in passive housing for the foundations. Insulating the foundations is vital to achieve a passive house rating and EPS is an excellent cost effective method of insulating your foundations and the good characteristics of strength, light and cheap makes EPS your best friend when insulating your foundations.

Like Polyiso EPS is easy to cut with a box knife or hand saw. EPS insulation does not have a foil attached to it so no need to score the insulation first before cutting it with a handsaw. Be careful however around any naked flames. Fire and EPS get on very well and EPS will burn and will billow out black smoke so if its does go up in flames stay away. Do not breath in the black smoke. If you take all the usual precautions when using EPS it will perform extremely well and will continue to do so with no depletion in performance over the duration of the life cycle of the building. Other insulations cannot boast such amazing lifetime performance.


Much like EPS in its appearance XPS is the big daddy of EPS. XPS is stronger, just as light and far exceeds its compressive strength of it EPS counterpart. XPS also gives a higher r-value but of course with all these fantastic additions to the insulation there is a price difference. XPS would be in the region of 20-30% more expensive than EPS. However XPS would be more widely used in the commercial / industrial insulation sector where compressive strength is a real requirement. Once again XPS like the other rigid board insulations is easy to cut and lightweight. XPS and EPS are closed cell insulation and will not lose their insulation values over time unlike Polyiso insulation which will deplete over circa 30 year period.

So what are the brands or who are the manufacturers of these products?

Polyiso: R-Max, Hunter, Owens Corning, Johns Manville and Dow are just some of the biggest Poyiso brands in the US.

XPS: Pactiv, Dow, Johns Manville and Owens Corning all manufacture XPS insulation.

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