What is the difference between polyisocyanurate and polystyrene?

When it comes to choosing insulation materials for buildings, polyisocyanurate and polystyrene are two names that often appear in homeowners’ and contractors’ search lists. Both are widely used in residential and commercial construction, but they have distinct characteristics that make them suitable for different scenarios. Understanding the difference between polyisocyanurate and polystyrene is not only essential for professionals in the construction industry but also for ordinary people who want to improve their home’s energy efficiency. This article will break down their differences from multiple perspectives—including composition, manufacturing process, thermal performance, fire resistance, durability, and application scope—so that even junior high school students can grasp the key points clearly.

First, let’s clarify what polyisocyanurate and polystyrene are respectively, as a clear understanding of their basic properties is the foundation for distinguishing them.

1. Basic Definitions: What Are Polyisocyanurate and Polystyrene?

Polyisocyanurate, often referred to as PIR in the industry, is a type of rigid foam insulation material. It is made by the reaction of polyol and isocyanate, with a closed-cell structure that gives it excellent thermal insulation and water resistance. During the manufacturing process, the raw materials undergo a chemical reaction to form a foam structure, and the addition of flame retardants further enhances its safety performance. PIR insulation board is widely recognized for its high thermal resistance, which means it can effectively prevent heat transfer and reduce energy consumption of buildings.

Polystyrene, on the other hand, is a common polymer material, and its insulation products mainly include two types: Expanded Polystyrene (EPS) and Extruded Polystyrene (XPS). EPS is the white foam material we often see in packaging and building insulation; it is made by expanding polystyrene beads with a foaming agent and then molding them. XPS, with a denser structure, is produced by extruding molten polystyrene with additives. Both EPS and XPS rely on the closed-cell structure in the material to trap air, thereby achieving the thermal insulation effect. Polystyrene insulation materials are popular for their low cost and easy processing.

From the basic definitions, we can see that although both are rigid foam insulation materials, their raw materials and manufacturing processes are quite different, which directly leads to differences in their subsequent performance. Next, let’s compare their core performance indicators one by one, which are also the key points that users care most about when choosing insulation materials.

2. Core Performance Differences: Thermal Insulation, Fire Resistance, and More

2.1 Thermal Insulation Performance: Who Is More Energy-Efficient?

Thermal insulation performance is the primary indicator of insulation materials, usually measured by thermal conductivity (λ value). The lower the thermal conductivity, the better the thermal insulation effect. This is a crucial factor for reducing heating and cooling costs of buildings, so it is the top concern for both contractors and homeowners.

The thermal conductivity of polyisocyanurate is generally between 0.022 and 0.028 W/(m·K). Its closed-cell rate is as high as 95% or more, and the tiny closed cells can effectively trap air, preventing heat convection and conduction. Even in low-temperature environments, the thermal insulation performance of PIR is relatively stable, and it will not decline significantly with the increase of service time. For example, in cold northern regions, using PIR insulation board for exterior wall insulation can reduce the heat loss of the building by 30% compared with some traditional materials.

Polystyrene’s thermal conductivity varies slightly depending on the type. The thermal conductivity of EPS is about 0.033 to 0.040 W/(m·K), and XPS is better, ranging from 0.029 to 0.036 W/(m·K). Although both have closed-cell structures, their cell density and uniformity are not as good as polyisocyanurate. Especially EPS, its thermal insulation performance is easily affected by moisture—if it absorbs water, the thermal conductivity will increase significantly. For example, if EPS is used in a humid basement without proper waterproofing, its thermal insulation effect may decrease by 20% to 40% after one year of use.

In summary, polyisocyanurate has better thermal insulation performance and stability, while polystyrene, especially EPS, is more sensitive to the use environment. For projects with high energy-saving requirements, polyisocyanurate is a more reliable choice; for low-budget projects with dry environments, polystyrene can also meet basic needs.

2.2 Fire Resistance: Who Is Safer in Case of Fire?

Fire resistance is another key performance indicator of building insulation materials, as it is directly related to the safety of people’s lives and property. The fire resistance of materials is usually evaluated by indicators such as flame spread rate, smoke generation, and whether they produce toxic gases.

Polyisocyanurate itself is a combustible material, but in the production process, manufacturers will add a large amount of flame retardants to improve its fire resistance. The modified PIR insulation board can reach the B1 level of flame retardancy (difficult to burn) in most cases. When exposed to fire, it will not burn violently, the flame spread rate is slow, and the amount of smoke generated is small. More importantly, it will not produce a large amount of toxic gases such as hydrogen cyanide, which can effectively buy time for personnel evacuation. Some high-end PIR products can even reach the A2 level of non-combustibility after special treatment, which is suitable for high-rise buildings and public places with strict fire safety requirements.

Polystyrene’s fire resistance is relatively weak. EPS and XPS are both flammable materials, and their flame retardant level is usually B2 level (flammable) if no special flame retardant treatment is done. When burning, they will melt and drip, which can easily spread the fire. At the same time, polystyrene will release toxic gases such as styrene and carbon monoxide when burning, which is a great threat to the respiratory system of personnel. Although some manufacturers will also treat polystyrene with flame retardants to improve its fire resistance to B1 level, its high-temperature stability is still not as good as polyisocyanurate. For example, in a high-temperature environment above 100°C, polystyrene will begin to soften and deform, while polyisocyanurate can maintain its shape and performance at temperatures up to 150°C.

In terms of fire safety, polyisocyanurate has obvious advantages. For buildings with strict fire protection requirements, such as hospitals, schools, and high-rise residential buildings, polyisocyanurate is more in line with the specifications; polystyrene is more suitable for non-key fire protection areas such as low-rise houses and temporary buildings.

2.3 Water Resistance and Durability: Who Can Serve Longer?

The service life of insulation materials is closely related to their water resistance and durability. Materials with poor water resistance are prone to aging and performance degradation after absorbing water, which shortens their service life and increases maintenance costs.

Polyisocyanurate has excellent water resistance due to its high closed-cell rate. The closed-cell structure can prevent water molecules from penetrating into the interior of the material, so even if it is used in humid environments such as roofs and basements, it is not easy to absorb water. The water absorption rate of PIR is generally less than 1%, and its performance can remain stable for more than 20 years under normal use conditions. In addition, polyisocyanurate has good chemical resistance and is not easily corroded by acids, alkalis, and other chemical substances, which further enhances its durability.

Polystyrene’s water resistance varies by type. XPS has a relatively dense structure, so its water absorption rate is low, about 1% to 2%, which is close to polyisocyanurate. However, EPS has a loose structure, and the connection between the beads is not tight, so its water absorption rate is relatively high, usually 3% to 5%. After absorbing water, EPS will become soft, and its thermal insulation performance and structural strength will decrease significantly. In terms of durability, the service life of polystyrene is generally 10 to 15 years, which is shorter than that of polyisocyanurate. Especially in outdoor environments exposed to wind, rain, and ultraviolet radiation, polystyrene is prone to aging and brittleness, and needs to be replaced regularly.

For long-term use and humid environment projects, polyisocyanurate has better durability; XPS can be used as an alternative in some dry environments, while EPS is more suitable for short-term or indoor insulation scenarios.

2.4 Structural Strength: Who Is More Resistant to Pressure?

Structural strength is an important indicator for insulation materials used in floors, roofs, and other places that bear pressure. Materials with high strength can avoid deformation and damage under pressure, ensuring the stability of the building structure.

The compressive strength of polyisocyanurate is generally between 150 and 300 kPa. Its internal structure is uniform and dense, so it has good load-bearing capacity. When used as floor insulation, it can bear the weight of furniture and personnel without deformation. In addition, PIR also has good bending strength, which is not easy to break during transportation and installation.

The structural strength of polystyrene also differs between types. XPS has high compressive strength, ranging from 200 to 500 kPa, which is even better than some polyisocyanurate products. Therefore, XPS is often used in floor insulation and roadbed insulation that require high load-bearing capacity. However, the compressive strength of EPS is relatively low, usually between 50 and 150 kPa, which is only suitable for scenarios with small pressure, such as interior wall insulation and packaging materials.

In terms of structural strength, XPS has advantages, while polyisocyanurate is in the middle level, and EPS is relatively weak. When choosing, it is necessary to select according to the actual pressure-bearing requirements of the project.

3. Cost and Application Scope: How to Choose Practically?

3.1 Cost Comparison: Initial Investment and Long-Term Benefits

Cost is often a key factor affecting the choice of insulation materials. We need to consider not only the initial purchase cost but also the long-term energy consumption and maintenance costs.

The initial purchase cost of polyisocyanurate is relatively high, usually 1.5 to 2 times that of EPS and 1.2 to 1.5 times that of XPS. For example, the price of a 50mm thick PIR insulation board is about $15 to $20 per square meter, while EPS of the same thickness is only $8 to $12 per square meter, and XPS is $12 to $16 per square meter. However, from the perspective of long-term benefits, polyisocyanurate has better thermal insulation performance, which can reduce energy consumption by 20% to 30% compared with polystyrene. Calculated based on the annual heating and cooling costs of a 100-square-meter house, the energy cost saved by using PIR can recover the initial investment difference in 3 to 5 years. In addition, the long service life of PIR also reduces the maintenance and replacement costs in the later period.

Polystyrene has the advantage of low initial cost, which is suitable for projects with tight budgets. However, due to its relatively poor thermal insulation stability and durability, the long-term energy consumption and maintenance costs are higher. For example, EPS used in exterior walls needs to be inspected and maintained every 5 to 8 years, and may need to be fully replaced after 10 years, which increases the overall cost.

3.2 Application Scope: Matching Materials to Scenarios

Based on the above performance differences, polyisocyanurate and polystyrene have distinct application scopes:

Polyisocyanurate is suitable for scenarios with high requirements for thermal insulation, fire resistance, and durability, such as:

• Exterior wall insulation of high-rise residential buildings and commercial buildings;
• Roof insulation of industrial plants and public buildings;
• Insulation of cold storage and refrigerated trucks that require low-temperature stability;
• Fire-sensitive areas such as hospitals, schools, and shopping malls.

Polystyrene (EPS and XPS) is suitable for scenarios with low budgets or specific requirements for strength, such as:

• EPS: Interior wall insulation of low-rise houses, packaging materials, decorative materials;
• XPS: Floor insulation of residential buildings, roadbed insulation, roof insulation in dry areas.

4. Environmental Protection: A Concern That Cannot Be Ignored

With the increasing awareness of environmental protection, the environmental performance of insulation materials has also become a concern for users. Environmental protection mainly involves the use of raw materials, the release of harmful substances, and recyclability.

The main raw materials of polyisocyanurate are polyol and isocyanate. In the production process, if environmentally friendly raw materials are used, the release of volatile organic compounds (VOCs) can be controlled within a low range. Most PIR products meet international environmental standards and will not cause pollution to the indoor environment. In terms of recyclability, polyisocyanurate can be recycled and reused after special treatment, but the recycling cost is relatively high, so the recycling rate is currently not high.

Polystyrene is a petroleum-based product, and its production process will consume a lot of non-renewable resources. EPS and XPS will release styrene monomers during production and use, which are harmful to human health if the content exceeds the standard. In terms of recyclability, polystyrene has good recyclability, and recycled polystyrene can be used to produce plastic products such as flower pots and plastic trays. However, due to the large volume and low recycling value of polystyrene insulation boards, the actual recycling rate is also not ideal.

In terms of environmental protection, both materials have room for improvement. However, with the advancement of technology, more and more manufacturers are developing environmentally friendly products, such as polyisocyanurate made from renewable polyols and polystyrene with low VOC emissions. When choosing, users can pay attention to the environmental certification of products, such as EU CE certification and US GREENGUARD certification.

5. Summary: How to Choose Between Polyisocyanurate and Polystyrene?

To sum up, the difference between polyisocyanurate and polystyrene is reflected in multiple aspects such as composition, performance, cost, and application scope. There is no absolute “better” between the two, only “more suitable” for specific scenarios. Here is a simple selection guide for reference:

• Prioritize polyisocyanurate if: High energy-saving requirements, strict fire safety standards, humid environment, long service life, and emphasis on long-term benefits;
• Prioritize XPS if: High structural strength requirements, dry environment, and moderate budget;
• Prioritize EPS if: Tight budget, indoor or short-term insulation scenarios, and low performance requirements.

No matter which insulation material you choose, it is necessary to purchase products from regular manufacturers to ensure product quality and performance. As a professional polyisocyanurate insulation board manufacturer, we provide high-quality PIR products with different specifications to meet the needs of various projects. If you have more questions about the difference between polyisocyanurate and polystyrene, you can contact our technical team for detailed consultation.