The selection of insulation materials in the construction of prefabricated modular buildings (such as modular dormitories, rotation camps, refrigerated container houses, mobile cold storage, etc.) directly determines the building’s energy consumption, service life and fire safety rating. The current market demand for insulation core materials is shifting from traditional PUR to high-performance PIR.

Based on the technical principles of rigid polyurethane foam and combined with combustion grade classification, this paper elaborates on the differences between PUR and PIR and their application value in prefabricated buildings in detail.

Based on the technical principles of rigid polyurethane foam and combined with combustion grade classification, this paper elaborates on the differences between PUR and PIR and their application value in prefabricated buildings in detail.

I. Core Chemical Structure: The Essential Differences Between PUR and PIR

Both PUR and PIR fall into the category of rigid polyurethane foams. They both take polyol and isocyanate as the main raw materials, and form different molecular skeletons through different formula systems, thus determining their physical properties and temperature resistance limits.

1. PUR Composite Board (Traditional Polyurethane)

Formula system: Polyether polyol formula is usually adopted.

Chemical characteristics: It has a low isocyanate index, and the skeleton structure of the foam is mainly composed of urethane segments.

Performance limitations: Due to the constraints of its chemical structure, the long-term service temperature of PUR products must be controlled below 100℃. In terms of flame retardancy, PUR usually needs to add a large amount of flame retardants to achieve a certain fire rating, which has limitations in high-temperature or open flame environments.

2. PIR Composite Board (Polyisocyanurate Modified Polyurethane)

Formula system: Polyester polyol formula is usually used with an extremely high isocyanate index (usually over 250).

Chemical characteristics: In the polymerization process, in addition to the formation of urethane segments, a large number of carbamate-modified isocyanurate segments are generated. This cyclic structure endows PIR with higher thermal stability.

Performance advantages: PIR products can be used for a long time below 150℃. Moreover, due to the introduction of heat-resistant and flame-retardant isocyanurate rings in the molecular chain, its inherent flame retardancy is far superior to that of PUR. When burning, a dense carbonization layer can form on the surface, effectively preventing the spread of flame.

II. Fire Rating: From “Additive Flame Retardancy” to “Structural Flame Retardancy”

Fire safety is an insurmountable red line in the material selection of prefabricated buildings. According to the Chinese national standard GB8624-1997 Method for Classification of Burning Behavior of Building Materials, materials are classified into the following grades:

• Grade A: Non-combustible materials (e.g., rock wool, stone)
• Grade B1: Flame-retardant materials
• Grade B2: Combustible materials
• Grade B3: Flammable materials

As organic materials, polyurethane (PUR/PIR) can reach a maximum combustion performance of Grade B1 (flame-retardant). A common misunderstanding needs to be clarified here: the PIR polyurethane cold storage board achieving Grade B1 is not simply realized by adding a large number of flame retardants, but stems from its special PIR formula system.

This structural flame retardancy technology makes PIR not easy to melt and drip when exposed to fire, and the carbonization layer can firmly lock heat and isolate oxygen, functioning like a “fire wall”. Therefore, in the current industry, prefabricated buildings with high insulation requirements and strict fire acceptance criteria (especially cold storage projects) generally require the use of PIR boards.

III. Application Recommendations: How to Select Materials for Prefabricated Buildings?

Based on the above technical analysis, the following material selection recommendations are put forward for different application scenarios of prefabricated buildings:

1. Ordinary Prefabricated Buildings/Modular Residences

Requirements: Mainly used for living or office with moderate temperature conditions.

Material selection: PUR composite boards can meet the basic insulation needs. PUR exhibits excellent insulation performance in non-extreme temperature difference environments with relatively controllable costs. However, it should be noted that if the project has strict fire rating requirements (e.g., requiring a Grade B1 test report), it is necessary to confirm whether the PUR board has passed the relevant flame retardant tests.

2. Prefabricated Buildings in High-Temperature Environments or with Strict Fire Rating Requirements

Requirements: For example, buildings close to heat sources, special industrial buildings, or projects requiring high-specification fire acceptance.

Material selection: PIR composite boards are recommended. The temperature resistance stability of PIR at 150℃ and its Grade B1 flame-retardant characteristics can provide double safety guarantees for the building. Its excellent dimensional stability also ensures that the board is not easy to shrink and deform during long-term use.

3. Cold Storage/Cold Chain Prefabricated Buildings

Requirements: Being in a low-temperature environment for a long time with huge temperature differences, which puts extremely high demands on the closed cell rate and water vapor permeability resistance of the insulation layer.

Material selection: PIR polyurethane cold storage boards are the first choice. As stated in the provided data, PIR polyurethane boards have become the best insulation material for cold storage construction. It not only solves the insulation problem at low temperatures but also raises the combustion grade to Grade B1, addressing the industry pain point that it is difficult to balance insulation and fire protection in cold storage.

IV. Conclusion

In the insulation material selection of prefabricated buildings, PIR is not simply an “upgraded version of PUR”, but a high-performance material improved based on chemical structure.

If you focus on cost performance and conventional insulation, PUR is a mature and reliable choice.

If you pursue long-term weather resistance, high-temperature stability and Grade B1 flame-retardant fire safety, PIR composite boards are undoubtedly the current market mainstream trend and technical guarantee.

With the continuous improvement of national standards for building energy conservation and fire safety, the application of PIR polyurethane boards in the field of prefabricated buildings will become more and more extensive. When purchasing, it is recommended to carefully check the material test reports to ensure that the selected boards truly meet the technical indicators of PIR and the combustion grade requirements of Grade B1.