Rigid vs. Blanket Insulation

Construction

• Rigid foam insulation can be made from several types of materials. Manufacturers produce molded expanded polystyrene (MEPS) foam board from liquefied and expanded polystyrene beads. Extruded polystyrene board (XEPS), which is similar to MEPS, is made from polystyrene pellets. Other rigid insulation materials are polyisocyanurate (polyiso) and polyurethane foam. Blanket insulation contains fiberglass, mineral wool or other flexible fibers, and may have a paper or vinyl facing. Manufacturers produce blanket insulation in rolls, which you can trim to fit a particular area.

Performance

• The R-value is a number that measures insulation’s resistance to heat flow per inch of thickness; a higher number indicates greater insulating performance. Manufacturers print the R-value on the label, on the packaging, on the facing or on the insulation itself. According to the United States Department of Energy, fiberglass blanket insulation has R-values between 2.9 and 4.3 per inch of thickness. Rigid insulation has higher R-values, ranging from 3.8 to 4.4 for MEPS boards and from 5.6 to 8 for polyiso and polyurethane boards.

Installation

• For best results, the Department of Energy recommends having a certified professional install rigid or blanket insulation. If you prefer to install the insulation yourself, you should be familiar with safety precautions as well as fire and building codes. Rigid insulation often requires a coating of tar or acrylic to protect it from damaging sunlight, or a vapor diffusion retarder to prevent excessive moisture buildup. Blanket insulation is suitable for installation in wall cavities, ceilings and timber floors and is available in widths that fit between floor joists or wall studs.

Benefits

• Rigid insulation adds strength to walls and roofs. In structural insulated panels, polyiso and polyurethane foams actually form part of the wall panel. Polyiso is especially suitable for roofs because it tolerates a temperature range between 100 degrees below zero to 250 degrees Fahrenheit. According to House Energy, blanket insulation is best suited for do-it-yourself ceiling, wall or floor projects. Some blanket insulation has flame-resistant facing and is particularly suitable for basement walls in which the insulation remains uncovered.

Considerations

• Rigid foam insulation burns quickly and emits a toxic smoke when it catches fire. Building codes require a 1/2-inch-thick gypsum wallboard as a fire barrier for foam insulation. Gypsum wallboard over interior foam insulation will also prevent insects from burrowing through foam board and reducing its insulating capacity. Avoid leaving air gaps, which can allow air and heat to flow in and out of the building, between blanket insulation and beams.