PUR and PIR are common rigid foam insulation materials with low thermal conductivity and low weight. They are widely used in industrial insulation and refrigeration. Their main differences lie in their chemical structures and thermal decomposition behavior, which also affect their fire performance and suitability for different applications.
PUR stands for rigid polyurethane foam, while PIR stands for polyisocyanurate foam. Both use isocyanates as an important raw material and share a common chemical basis.
PUR was industrialized earlier. As demand for improved thermal stability and fire performance increased, PIR materials developed through changes in the reaction system and promotion of isocyanate trimerization gradually gained wider use.
◆ Note: It is important to note that commercial PIR foam can also contain polyurethane structures. Therefore, PUR and PIR are not completely separate material systems. Rather, they are rigid foam materials with different proportions of chemical structures and different performance characteristics.
PUR is mainly formed through the reaction of isocyanates with polyols to produce polyurethane structures. PIR is produced by promoting isocyanate trimerization to form a higher proportion of isocyanurate ring structures.
PIR generally provides better thermal stability and fire performance, although the actual properties depend on the formulation, manufacturing process, and product structure.
Both materials can provide effective thermal insulation. Their actual thermal conductivity depends on factors such as cell structure, density, blowing agent, and service conditions, so it should not be determined solely by the material type.
The isocyanurate ring structures in PIR have relatively high thermal stability. Compared with foams based primarily on polyurethane structures, materials with a higher proportion of isocyanurate structures generally have greater resistance to thermal decomposition.
When exposed to flame or high temperatures, PIR generally has a stronger tendency to form a char layer. This char layer can help slow heat transfer into the underlying material and limit the release of some combustible decomposition products, thereby improving its combustion performance.
However, fire performance should not be confused with non-combustibility, and the foam's combustion behavior does not directly represent the fire rating of a complete insulation system. Flame retardants, material density, facing materials, and system construction also affect actual performance and should be verified through relevant test results.
PUR is commonly used for insulation of industrial equipment, pipelines, cold storage facilities, and refrigeration systems. It can be suitable for projects where thermal insulation, mechanical performance, weight, processing, and installation requirements need to be considered together.
PIR can be used for insulation of petrochemical facilities, ethylene units, industrial equipment, and pipelines, particularly where higher thermal stability and fire performance are required.
◆ Note: The application ranges of PUR and PIR overlap, so material selection should not be based solely on the industry or equipment type.
▸ Step 1 — Start by confirming the design temperature and operating conditions, then review the product's thermal conductivity, mechanical properties, and applicable service temperature range.
▸ Step 2 — If the project has specific fire safety requirements, also check the relevant test reports and applicable standards.
▸ Step 3 — For low-temperature and cryogenic applications, additional consideration should be given to low-temperature performance, joint treatment, and the design of the complete insulation system.
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