Mule-Hide Blog

Back to Blog

Polyiso is the Low-Slope Roofing Insulation Workhorse

Posted: 11/30/2023
Polyiso is the Low-Slope Roofing Insulation Workhorse

Insulation is an essential component in any low-slope roof. It serves as a buffer, keeping conditioned air inside the building and bitter cold or sweltering hot outdoor air out, reducing heating and cooling costs while ensuring occupants’ comfort. And in cold climates, it works with the vapor retarder to keep the moisture in warm indoor air from condensing and accumulating in the roof assembly.

There are a variety of insulation options, including polyisocyanurate (polyiso) boards, expanded polystyrene (EPS) boards, extruded polystyrene (XPS) boards, spray polyurethane foam (SPF), lightweight insulating concrete, mineral wool and fiberglass. Polyiso is the industry workhorse, thanks to its combination of versatility, high R-Value and moisture-resistance, and is the most commonly used.


What is Polyiso?
Polyiso insulation boards consist of a closed-cell polyisocyanurate foam core sandwiched between two facer sheets. The closed-cell structure of the foam – in which the cells are pressed tightly together – prevents air and moisture from permeating the foam and makes the board rigid.


A Versatile Solution

Polyiso boards are at home on virtually any low-slope roof. They can be used in new construction, to recover an existing roof, or as part of a full tear-off and replacement. They are compatible with modified bitumen and single-ply membranes and the accessories used with them. They are approved for inclusion in fully adhered, mechanically attached and ballasted single-ply systems.

Boards are available in a range of thicknesses and compressive strengths and can be layered, providing tremendous flexibility in designing a system to meet a project’s specific needs. Flat panels are appropriate when the roof already has adequate drainage, and tapered systems can be designed to provide additional drainage where necessary.


Highest R-Value

Inch-for-inch, polyiso delivers the highest R-Value. As shown in this chart from the Certified Commercial Property Inspectors Association, at a mean temperature of 75 F, it has an R-Value of 5.6 to 6.7 per inch, compared to 5.0 to 5.6 per inch for XPS, 3.9 to 4.7 per inch for EPS, and 3.6 to 6.7 per inch for SPF.


Excellent Moisture Resistance

Polyiso’s closed-cell structure makes the boards moisture-resistant. Even boards with standard paper facing outperform EPS boards, which can become saturated quickly, creating a perfect environment for mold to flourish. Add glass facing to polyiso boards, and moisture has an even harder time finding its way in.


Options for any Project

Mule-Hide Products offers flat and tapered polyiso insulation boards to meet the needs of any project. Boards are available in a variety of thicknesses in compressive strengths of 20 psi and 25 psi. All feature a closed-cell polyiso foam core laminated to heavy (non-asphaltic) glass fiber-reinforced felt facers to provide maximum moisture resistance.

Learn more here.

Back to Blog

Theme picker