Polyisocyanurate (Polyiso) is a closed-cell, rigid foam board insulation that is bonded to facers on both sides, which are composed of various organic and inorganic materials. It is used in roof, wall, ceiling, and specialty applications within commercial and residential buildings of all types.

Polyisocyanurate is most commonly used as continuous insulation for roofs and walls, and as a protective roof cover board.

Polyisocyanurate Insulation in Roofing Applications

Commercial roofs are subjected to full assembly fire testing. Individual material components like Polyiso insulation are required to meet additional product-specific fire performance criteria.

Polyiso remains the only foam plastic insulation product for direct application to steel roof decks to earn FM Approval for Class 1 Roof Systems. An FM Class 1 designation means the roof assembly has been subjected to a series of tests in addition to external and internal fire exposure. This includes:

  • Wind uplift
  • Water leakage
  • Impact resistance

As a result, direct-to-deck assemblies containing Polyiso insulation meeting NFPA 276 (FM 4450) or UL 1256 can be installed without a thermal barrier.

To date, hundreds of thousands of assemblies have gained approval under these test standards.

Polyisocyanurate Insulation in Wall Applications

Exterior walls of any height on commercial buildings (IBC Types I-IV) that contain Polyiso insulation (or any other foam plastic insulation) must be evaluated for full-assembly fire performance per NFPA 285.

Foam plastic insulation products are also required to meet additional product-specific fire performance criteria for flame spread and smoke development. Polyiso’s exceptional fire performance provides building designers with important flexibility when selecting other components of exterior wall systems, including façade or cladding materials.

A wide variety of exterior wall assemblies that combine Polyiso insulation with MCM panels, brick, and other popular materials have passed the rigorous, two-story NFPA 285 fire test.

Note: Wall systems containing Polyiso insulation may be subject to other fire tests and building code requirements. Consult your local building code and manufacturer installation instructions for more details.

Unique Properties of Polyisocyanurate

Polyisocyanurate’s unique chemistry, R-value, and fire performance make it ideal for continuous industrial applications (for those customers whose outside temperatures do not dip below 50°F or 10°C).


An insulation material’s resistance to heat flow is rated in terms of R-value – a higher R-value means greater insulating effectiveness (i.e., higher resistance to heat flow).

It is important to note that Polyiso’s R-value increases with thickness.

For example, a two-inch Polyiso product has more than twice the insulating value of a one-inch product. The increase in thermal resistance for thicker products is due to the reduced contribution of more thermally conductive elements such as the facer and the denser cell structure in the foam near the surface.

Continuous Insulation

Continuous insulation means that the material is continuous across all structural members without thermal bridges other than fasteners and service openings.

Applications for continuous insulation include:

  • Above-grade walls
  • Roofs
  • Below-grade walls

The uninterrupted thermal barrier across these surfaces increases the effective R-value of the building assembly as compared to adding a similar amount of non-continuous insulation (such as within stud cavities).

Polyisocyanurate continuous insulation (Polyiso CI) delivers a high R-value when compared to other products, which means the designed thermal performance of the building assembly can be achieved with a minimum thickness of insulation. Thinner insulation results in thinner profiles for exterior wall and roof assemblies.

A popular application for Polyiso CI is exterior wall assemblies for residential and commercial buildings. For wall applications, Polyiso CI can be installed as a 3-in-1 building envelope solution to:

  • Reduce energy loss
  • Decrease air leakage
  • Minimize moisture intrusion

Fire Performance

An important consideration for building assemblies – especially the wall assemblies of multi-story commercial buildings – is fire performance.

Polyiso CI possesses a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved resistance to high-temperature exposures as well as enhanced fire resistance.

All construction materials, including foam plastic materials like Polyiso insulation, must provide a suitable margin of fire safety. Codes and test standards set the minimum level of overall building fire safety as well as minimum levels of fire performance for specific construction materials and assemblies. These codes and standards are developed and maintained through consensus-based processes.

Groups of experts and other stakeholders that include representatives beyond product manufacturers contribute to the various code and standard development processes.

Polyiso insulation delivers a high level of inherent fire resistance when compared to other foam plastic insulations due to its unique structure of strong isocyanurate chemical bonds. These bonds result in improved high-temperature resistance (up to 390 degrees F; more than twice the temperature resistance of other building insulation foams) which in turn leads to enhanced fire resistance. Polyiso also forms a protective surface char when exposed to a sufficient flame source.

Benefits of Polyisocyanurate Insulation

To recap, Polyiso benefits include:

  • Highest R-Value per inch of any insulation product. (R-value – 6.0 per inch)
  • Absorbs less than 1% of water, far less than any other rigid insulation
  • Relatively strong at 20 psi
  • Holds up well and can be reused where complete roof tear-offs are not required
  • Lightweight and easy to install

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