What Is Rigid Insulation?


Rigid insulation is a construction material used in residential and commercial structures. It is designed to improve the thermal resistance of a building, which can improve the comfort levels of occupants while providing a number of environmental benefits. This material consists of rigid foam boards, which can function as both insulating and structural components depending on the application.


  • Rigid insulation is made from a closed cell foam that is typically sold in 1-inch thick sheets. Because of its closed cell structure, it is considered a highly effective insulator. The ability of a material to insulate a building is known as thermal resistance, and is measured using a rating known as R-value. The higher the R-value of a material, the better it can resist thermal transfer. Rigid foam has an R-value between 4 and 6 per inch of thickness. This is roughly twice the R-value of other insulating materials.


  • Sheets of rigid foam insulation are cut to size and installed in many different applications. One of the most common installations is within wall cavities, where the foam sheets are nailed or screwed to wall framing members then covered by drywall. They may also be installed on top of roof sheathing before shingles or roof panels are installed. Rigid insulation is commonly used to insulate garage doors, garages, and attics.


  • There are three basic types of materials used to make rigid insulation. The most affordable is molded expanded polystyrene (MEPS), and is commonly referred to as "beadboard." Most MEPS should not be used in structural or roofing applications. Extruded expanded polystyrene (XEPS) is slightly more expensive, but also denser and a better insulator. Polyurethane foam boards have the highest cost of the three, along with an R-value as high as 7 or 8 per inch.


  • The rigid quality of foam insulation provides a number of advantages. First, it provides some structural support for the building, and can be used to brace the framing system. It tends to keep its shape and will not sag like batt insulation. This helps reduce air leaks over time. Rigid insulation also offers a high R-value per inch and is a good material for insulating tight spaces. Finally because of its high R-value, rigid insulation can significantly reduce energy consumption. This can help lower utility bills and protect the environment.

Special Applications

  • Rigid insulation is used in several specialty products that are designed to maximize energy efficiency. Structural insulated panels (SIPs) are made from rigid foam insulation sandwiched between sheets of oriented strand board. These panels are used to frame walls, ceilings, and roofs in homes. The high R-value of the foam makes SIPs a particularly good option for those looking to go green. Foam panels are also used to create integral concrete forms (ICFs). These forms are similar to SIPS, but are designed to form cast-in-place concrete. Once the concrete is poured, the foam insulation and form stay in place to create highly insulated floors and walls.

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