For a while there, there were many questions about the performance of rigid foam insulation and how it holds up in various applications. After extensive research, we thought we'd share the details of how they perform vs each other and the arguments favouring each type. We hope this helps you decide which insulation is suitable for your application.
PIR and PUR
One of the most common ways to weatherize a home is PIR (polyisocyanurate) and PUR (polyurethane) boards. The two building materials are very similar but offer different benefits. PIR boards are rigid and lightweight, while PUR boards are flexible and resistant to mould. PIR boards are ideal for insulation of exterior walls and floors, while PUR boards are a better choice for interior walls and ceilings
If you're looking for a form of insulation that provides double the R-value of fibreglass, foam insulation is the way to go. Depending on the manufacturer, PUR and PIR insulation can be placed on just about any surface and is not too susceptible to mold or moisture.
EPS
Expandable polystyrene (EPS) is a great insulator, but it isn't a great conductor of heat, so heat is trapped in the attic. You can cover your ceiling with fibreglass insulation, but the insulation board is not conductive enough to prevent cold spots. If the attic is uninsulated, the only way to ensure that the attic does not get too cold is with heat.
The most effective way to insulate your home is by including a layer of insulation behind the walls. This is often done with a layer of expanded polystyrene (EPS) insulation board. Some people feel a fair bit to be said for installing it in the cavity between the floor and the ceiling.
Case Study:
Fred's installation was done mainly with rigid foam blocks, but some of the site's windows were also insulated with spray foam. Both types of insulation perform their task admirably, but the foam blocks are easier to install, and in some instances, the cost savings is marginal to none. This is true when you consider that one tonne of rigid insulation will typically cover about 1,000m2.