Homeowners and builders have several options available to them when deciding on which thermal insulating material to use for a home, commercial or industrial application. Thermal insulation reduces energy costs, keeping your home warm in the winter and cool in the summer. It reduces the heat transfer between two objects of different temperatures, such as your home and the environment. In order for a material to be used as thermal insulation, it must limit the heat convection, conduction, radiation or a combination of the three. Additional benefits of a good thermal insulator include energy conservation and temperature control of surface temperatures.
Other factors in addition to insulation material must also be considered to keep a building comfortable. Heat transfer and temperature distribution of other building materials, changes in moisture levels, as well as solar radiation and other internal heat generation sources are also important.
The measure of a thermally insulating material's resistance to heat flow is referred to as the R-value. The higher the R-value, the greater the effectiveness and the higher the resistance to heat flow. Care must be taken when installing to follow manufacturer’s instructions. Incorrect installation, such as excessive material compression can reduce the efficiency.
Variations in climate conditions and building materials yield differences in suggested R-values. The map and table below indicate R-value and heat system recommendations for wood-frame houses in the continental United States.
The zone in the table below refers to the zones numbered in the map above. Alaska falls under Zone 7, except for Bethel, Northwest Arctic, Dellingham, Southeast Fairbanks, Fairbanks N. Star, Wade Hampton, Nome, Yukon-Koyukuk and North Slope, which are covered under Zone 8. The southern tip of Florida, Hawaii, Guam, Puerto Rico and the Virgin Islands are in Zone 1.
Adding layers of insulation can further reduce heat flow and increase efficiency. R-values of multilayer insulation materials can be added together to determine the overall R-value of the system.
Thermal Insulation Materials
The most common insulating materials on the market today are:
- Mineral wool
- Polyurethane foam
- Expanded polystyrene (EPS)
- Extruded polystyrene
Fiberglass insulation, which is sometimes referred to as glass wool, is easily the most common insulating material on the market, due in part to its low cost. Fiberglass is made by combining glass (35% or more of which is recycled glass), sand, soda ash, limestone and other minerals. The mixture is heated to a molten form and then fed to a spinning bowl where fine threads of glass are formed and woven together. The spinning process is similar to the one used to make cotton candy, and the end products of the two even have a similar appearance. Fiberglass insulation is nonflammable and does not absorb water. R-values for fiberglass insulation vary depending on the density and material thickness. With values of R-2.8 to R-3.8 per inch of material, R-values can range from R-11 for 3 ½ inches thick to R-38 for 12-inch thick material.
Purchase options for fiberglass insulation include batts, blankets, rolls and loose fill.
Batts, blankets and rolls are all rectangular sections of material and are the most common form of thermal insulation. Standard widths and thicknesses make them easy to handle and install between studs and joists. Common applications for batts and blankets include unfinished floors, ceilings and walls. To avoid compromising efficiency, cut fiberglass insulation around pipes and other obstructions instead of compressing it.
Loose fill refers to insulation not formed or packaged into a standard shape. While hand installation of loose fill is possible, the most common method is blown it in using an insulation blower. Common applications for loose fill include walls and attics. An advantage of loose fill is that that the insulation can fill voids and works well in spaces with pipes and other irregular shapes.
To avoid discomfort due to the tiny glass fibers, wear protective clothing, gloves and eyewear when handling fiberglass insulation. Failure to take proper precautions can lead to eye, lung and skin damage.
Compressing fiberglass insulation during installation may reduce the R-value. Be sure to cut fiberglass batts or rolls around pipes and other obstructions instead of compressing it to maximize efficiency. Fiberglass batts are manufactured with a foil or kraft paper vapor retarder surface.
Mineral wool is an insulation material manufactured from natural or synthetic fibers such as slag or ceramics. After heating to a molten form, the fibers are woven together by a process referred to as melt spinning. It is then sold as loose fill or formed into batts or boards for use as insulation. Mineral wool batts have a slightly higher R-value than fiberglass batts of equivalent thickness. For example, a mineral batt for 2x4 construction wall construction has an R-value of 15 compared to 11 or 13 for fiberglass or cellulose. While mineral wool has been around for many years, it is becoming a popular option again. There are several reasons for this, including:
- Most mineral wool manufactured today is made from recycled content.
- Mineral wool is not combustible.
- Mineral wool is denser than fiberglass insulation and can be marked to the desired size and cut with a saw.
- Mineral wool is easier to install than fiberglass and stays in place without support.
- Mineral wool is more expensive than fiberglass but less costly than spray-in foam.
- Mineral wool hold its shape in the event of a fire, helping protect against the spread of the fire.
As with fiberglass insulation, proper clothing, eyewear, masks and gloves should be worn to prevent insulation ingestion, eye injury or itch associated with handling the material. Vapor retarders must be used with mineral wool batts and boards, as they are not manufactured with a foil or paper retarder like fiberglass.
Cellulose is an inexpensive loose fill insulation, most commonly used as a blow-in material. Cellulose is environmentally friendly as it is manufactured from recycled cardboard, paper and other similar materials. It is a tightly compacted material that contains practically no oxygen, making it an excellent material for fire resistance. In addition to unfinished attics, cellulose can be installed into walls or ceilings of existing structures by blowing it in through small holes drilled from the exterior of the house. Cellulose has an R-value of R-3.1 to R-3.8 per inch of material.
There are a few possible disadvantages of cellulose, including allergy concerns for people allergic to paper dust, and obtaining skilled labor may be more difficult than it is for fiberglass. Additionally, due to the dense nature of the material, it may be too heavy for attics with drywall less than 5/8 inch thick. Cellulose also has a tendency to compress over time, which reduces efficiency.
Applied with a spray gun, polyurethane foam is excellent for filling around pipes and getting into tiny crevices. Although installation costs are higher than fiberglass or cellulose, polyurethane foam is also one of the most efficient types of insulation. The foam expands after spraying to fill every crack and air gap and then hardens to keep its shape. Environmentally friendly foaming agents that do not harm the ozone layer have started to replace harmful chlorofluorocarbon (CFC) and hydrochlorofluorocarbon (HCFC) aerosol propellants commonly used in liquid spray foam insulation.
Spray polyurethane foam (SPF) is the most common liquid spray foam for wood-structure buildings. Polyurethane foam has a relatively high R-value of R-3.4 to R-6.7 per inch of material and blocks conductive, radiant and convective modes of heat transfer. Two different types of SPF are available, a medium-density closed-cell spray foam (ccSPF) and a light-density open-cell spray foam (ocSPF). Open-cell foam lets moisture in, but keeps air out, while closed cell foam stops both moisture and air. The ocSPF carries a lower R-value (~R-3.8) than the ccSPF and is crushable by hand. Closed-cell foam is more rigid and is also more expensive, but carries a higher R-value (R-5.0 to R-6). Building insulation applications for polyurethane spray foam include ceilings, walls and attics.
Expanded Polystyrene (EPS)
Expanded polystyrene (EPS) is a lightweight, rigid, closed-cell insulation material manufactured in many different densities to resist compressive loads. EPS is made from molten polystyrene beads that are formed into blocks or boards. EPS can be cut with a saw and resists water absorption and vapor penetration. EPS building insulation applications include roofs, attics, foundations, wall insulation and slab insulation. The R-value of EPS is a relatively high value of R-4.6 per inch of material, which does not degrade over time. Another benefit of EPS is that it does not support the growth of mold or mildew. Extended exposure to the sun will degrade the product. Expanded polystyrene is also commonly used for drinking cups, packaging and coolers. It is commonly, and incorrectly, referred to as StyrofoamTM.
Extruded Polystyrene (XPS)
While extruded polystyrene (XPS) resembles EPS, it is manufactured using a different process. XPS is sometimes referred to as StyrofoamTM, which is a trademarked extruded polystyrene material owned by The Dow Chemical Company. XPS is easily visually distinguished from EPS material by its color. EPS is white, while XPS is blue, green or pink. XPS is recyclable and commonly used in below-grade applications. It has a fairly high R-value of 5 per inch. XPS retards water but is not considered a water barrier, and it does not support the growth of mold or mildew. Extended exposure to the sun will degrade the product.
Several other types of foam materials are available, including polyisocyanurate, cementitious and phenolic (see Phenolic Insulation: A Wise Choice For Chilled Water Piping). Other, less common types exist as well.
Many different types of insulation materials are available, each with pros and cons.
Fiberglass is inexpensive, non-flammable, environmentally friendly and readily available. However, it is more difficult to work with and easily compressible, which degrades the efficiency.
Mineral wool is easier to work with than fiberglass and carries a slightly higher R-value but requires the same precautions when handling it. It is environmentally friendly and neither flammable nor combustible but is more expensive than fiberglass.
Cellulose is relatively inexpensive and environmentally friendly but more costly than fiberglass and is not fireproof. It has a higher R-value than fiberglass or mineral wool, but can be problematic for people with allergies, tends to compress over time and may be too heavy for some applications.
Polyurethane foam is an excellent insulation with good R-values but is expensive, difficult to install and not environmentally friendly.
Expanded polystyrene (EPS) has good long-term and stable R-values, does not support the growth of mold or mildew and is inexpensive. However, it is not environmentally friendly and is flammable.
Expanded polystyrene (XPS) has good long-term and stable R-values and does not support the growth of mold or mildew. It is a good below-grade insulation.
The pros and cons of the various insulation material should be considered, along with their cost, R-value and your geographical location when selecting the appropriate thermal insulation material for your application.