Polyisocyanurate, Extruded Polystyrene, Expanded Polystyrene

Rigid insulation is often used for foundations and as an insulated wall sheathing.  It is made from fibrous or plastic foams and is produced in board-like forms.  These boards can provide full coverage with little heat loss paths and can provide a greater R-value where depth is limited.  Some rigid board insulation is faced with a reflective foil that reduces heat flow when next to an air space.

It is important to understand the differences between the types of rigid insulation to select the proper product for your job.  There are a variety of board types as well as a variety of brands.

Polyisocyanurante – “Polyiso” has the highest R-value per inch of any rigid insulation (as high as 6 per inch).  It typically has a reflective foil surface.  Certain lines of Polyiso are suitable for exposed use.

  • Rmax – Thermasheath-3     
  • Dow – Thermax
  • Johns Manville – AP Foil

Extruded polystyrene – (XPS) is usually pink or blue in color with a smooth surface.  XPS panels typically are not faced with any other materials.  R value is about 5 per inch.  This foam will not absorb water like polyiso and is stronger than Expanded polystyrene (EPS).  It usually comes in 2’x8’ and 4’x8’ in thicknesses of ¾”, 1”, 1 ½”, 2”, 2 ½”, 3”, 4” and is available in high-load/PSI alternatives.

  • Dow Blue Board

Expanded polystyrene – (EPS) is the most common and least expensive rigid insulation and has the lowest R value around 3.8 per inch.  It comes is a variety of sizes and custom lengths

  • Insulfoam