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Advantages of PIR Insulation over Polystyrene

Thermoset vs. Thermoplastic--Is Your Value Melting Away?
Foam plastic insulations are either thermoplastic or thermoset materials. PIR insulation products are thermoset, which means that once manufactured, they are rigid, will not soften or melt and remain strong, even at elevated temperatures. They can withstand elevated temperatures without losing their insulating power. Extruded polystyrene is a thermoplastic material which softens at 165°F and melts in the 200°F to 210°F range.

Is Your Insulation Affected by Construction Materials?
Extruded polystyrene can be attacked by many petroleum based solvents in adhesives, paints, stains, water repellent and preservative coatings, and in bituminous waterproofing. Solvents should be allowed to evaporate before touching the foam. As many contractors have discovered, the application of these common construction materials causes the extruded polystyrene to dissolve. This problem is solved by using PIR insulation. It is not affected by these materials and therefore offers a level of comfort that the insulation value you purchase today will remain in place year after year.

Ultraviolet Light--What's the Effect?
Ultraviolet light degrades extruded polystyrene. When installed on the job and left exposed to the rays of the sun, the surface of extruded polystyrene becomes yellow and dusty. In these cases, you can take a brush and dust the insulation value right off the extruded polystyrene board. The faces on PIR insulation protect the foam core from UV degradation.

Thermal Performance--On a per inch basis, PIR always exceeds polystyrene!
In every recommended application, PIR insulation delivers more R-value per inch of thickness than extruded polystyrene products. For example, when both products are used as wall sheathings, the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) Design R-value for foil faced PIR is 7.04 per actual inch versus 5.0 for polystyrene, when tested at 75°F means temperature--a benefit of 40% for PIR!

In roof applications, permeable facers are preferred and the average thickness of foam used is 2 inches. At this thickness, the advantage in thermal performance of PIR over polystyrene is a t least 40%. This benefit produces meaningful savings in energy consumption as well as installation costs.

Does Moisture Matter?
Moisture can be present in a wall or roof system as liquid water or water vapor--two distinct and separate phases of water that can behave very differently. The real enemy of insulation performance is water vapor. If water vapor passes into and condenses in an insulation, the overall thermal performance will decrease. The questions are:

  • Will water vapor pass into and condense in insulation used as sheathing?
  • How can you determine if insulation is prone to water vapor problems?


The real measure of a material's resistance to water vapor is through testing the product via ASTM E96, a measure of water vapor transmission. This method produces permeance ratings, or perms. Typically, PIR foil faced sheathings have perm ratings of less than 0.03, (water vapor transmission = 0.0 g/hr.m2 for PIR of panel 50mm thick) or 22 times better than extruded polystyrene. This means extruded polystyrene is more likely to let water vapor penetrate into their cells. If this happens and the dew point temperature is reached, water will condense inside the cells reducing the insulation value. Liquid water should never be present in a building system. If an insulation, PIR or polystyrene is submerged in water, there is no insulation benefit as the water short circuits around the insulation. Insulations must be kept dry. If minor contact does occur, the foil facings and closed cells of PIR provide excellent water resistance.