Rock Wool Insulation Vs. Fiberglass Insulation

Rock wool and fiberglass insulation provide thermal barriers to minimize heat loss in walls, ceiling, floors and attics. Insulation provides property owners with a cost-effective method for making structures energy-efficient. Combined with other insulating components, such as doors and windows, property owners can realize significant savings on energy costs.

Rock Wool or fiberglass insulation can also Insulation also function as sound barries to minimize the transfer of unwanted noises.


Rock wool is created from basalt or diabase -- materials resulting from volcanic eruptions. The U.S. Patent Office granted a patent for rock wool as a commercially viable product in1875. The material has a wide range of applications, including insulation for pipes, vessels and industrial buildings. In the last 10 years, builders have increased the use of rock wool in residential new construction. Manufacturers make fiberglass insulation from fine molten glass fibers. Fiberglass came into its modern form in 1932. Residential Design and Build magazine cites a 2008 study by the Freedonia Research Group, which states fiberglass insulation makes up about 85 percent of the residential insulation market in the United States.


Both products come in loose-fill or blanket/batt form. Insulation manufacturers make blanket/batt insulation faced or without a face. The faced product has a covering that functions as a vapor barrier. The vapor barrier prevents moisture from penetrating the material. Many do-it-yourself homeowners complete blanket/batt insulation jobs. The material has naturally fire-resistant qualities, but does not install as airtight as rock wool. Moisture can compromise the effectiveness of fiberglass insulation, and it has a tendency to attract rodents seeking a place to nest. Concern exists about the possible health effects of fiberglass insulation and the release of formaldehyde and tiny particles. Do not install fiberglass insulation near heat-producing appliances or fixtures. Rock wool's recyclable quality makes it environmentally friendly. It retains its thermal qualities after exposure to moisture and can come in close contact with chimneys or stoves. Mineral wool costs about 10 percent more than fiberglass; it does not release harmful fibers or emissions. Depending on the local building codes, the project may require the installation of a vapor barrier.


The R-value measures the capacity for insulation to resist heat flow. Higher R-values slow down cold and heat flow due to greater insulation power. Rock wool has an R-3 to R-4 value per inch of material. Fiberglass has an R-3 value for each inch of insulation. Installers can purchase blanket/batt insulation that comes in R-values, such as R-11, R-22 or R-30. The recommended R-value depends on the location and the building components insulated.

Installation Methods

Batts come in lengths of 4 or 8 feet. Installers must cut blanket insulation to the desired length. The width of the material allow the installer to fit snugly in cavities between studs, joists or beams. Insulation projects with blankets or batts require opened walls, floors or ceilings. The material loses it effectiveness if gaps exist between the sheets. Follow the manufacturer instructions for installing and sealing. Rock wool or loose-fill insulation work effectively for open new walls and between cavities of enclosed walls. One installation technique utilizes an insulation blowing machine and hose to blow the insulation in place. This ensures coverage around pipes, cable, electrical boxes and other objects. Many installers simply pour loose-fill material in place for certain projects like insulating an attic floor.