What is the difference between polyurethane (PUR) and polyisocyanurate (PIR)?

What is the difference between polyurethane (PUR) and polyisocyanurate (PIR)?

Rigid polyurethane foam is a high-performance material for Insulating Panels and construction. Both polyurethane rigid foam (PUR) and its variant polyisocyanurate or rigid polyiso foam (PIR) display excellent thermal insulation properties – but do you know the difference between them, and why should it matter?

Rigid polyurethane foam is a highly cross-linked thermoset plastic of low density. The low thermal conductivity of the blowing agent contained in the cells is responsible for the material’s excellent insulating properties. Rigid polyurethane foams are used to prevent energy loss and minimise CO2 emissions applications that require thermic insulation.

At a quick glance, polyisocyanurate or rigid polyiso foam, known as PIR, appears to be the next generation development of the classic polyurethane rigid foam or PUR in short. Both foams are manufactured using the two components isocyanate (MDI) and polyol.

The Isowall structural composite panel consists of a core of thermally efficient insulation material sandwiched between two outer pre-stressed skins and bonded to them. This gives the panel its impressive strength characteristics. Various facing materials and finishes are available.

It is this particular composition of MDI and polyol that determines the variance. During foam production, the reaction mix enables the forming of strong, permanent bond with any facings. The foam structure and bonding properties determine the best product application.

PUR has a balanced structure. Its components MDI and polyol are distributed at a uniform ratio compared to their molecular masses. The classic structure displays great insulation properties. As a result, PUR has been used in the construction industry for decades as a high-performance insulation material.

By comparison, PIR contains an excess of the MDI component, which causes a different reaction between its two elements, MDI and polyol, now unbalanced. This reaction leads to the PIR foam, an enhanced form of PUR, a heavily linked synthetic material with ring-like structures that is very rigid and highly stable due to the raised level of linkages.

The new substance PIR, obtained from continuous technical development of PUR over decades, has superior firmness, strength, thermal resistance and dimensional stability.

At Isowall we use PUR as floor insulation and PIR as a sandwich panel core material.


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