fiberglass vs. Rockwool insulation

Fiberglass and mineral wool (that is, rock-woll and slag-wool) are very similar as insulation materials, both in their uses and forms.

Fiberglass vs. Rock wool and slag wool

Fiberglass is by far the most common insulation material worldwide, and it is made from molten glass - while rock wool is made from molten rock. Rockwool/mineral wool is much less common, namely in USA. It's in Europe, Australia, Canada and New Zealand that rock wool is mostly used.

Both are sold in batts/rolled blankets or as loose-fill fibers, and their manufacturing is very similar.

The uses of fiberglass and Rock wool

As fiber insulation materials, fiberglass, rock wool and slag wool are particularly suited to insulate irregularly shaped areas, hard-to-reach places, areas with obstructions and unfinished attic floors and wall cavities.

Fiberglass and rock wool blankets and batts are commonly used in foundations and unfinished walls, ceilings, attics and floors. They are installed between studs, joists and beams, namely in standard spacing cases, free from messy obstructions.

Installation

Fiberglass and rock wool blankets and batts installation is a do-it-yourself job, contrarily to loose-fill installation.

Inadequate installation will lower the insulation effectiveness. Batts should be well fitted with the surrounding structures.

Fiberglass and rock wool fiber, on the other hand, demand special equipment to be blown into place, and some know-how about the right thickness and application rules… It's not a DIY job. See: Fiber insulation.

Efficiency and Prices: Rock wool vs. Fiberglass

Rockwool R-value (efficiency) is slightly higher than that of common fiberglass: approximately R-3.7 per inch, which amounts to high-density fiberglass batts or cellulose R-values.

Mineral wool has a higher density, and can provide better acoustical and insulating results than fiberglass. Besides, mineral wool doesn’t lose its insulating value when wet, and has an outstanding resistance to fire.

The mainly disadvantages of rockwool (vs. fiberglass) is that its prices are higher - largely because it is a less common insulation material...

Safety

Rock wool and fiberglass are both very safe insulation materials.

Some health experts claim that fiberglass fibers, when inhaled, are carcinogenic. But institutions as the American Lung Association state otherwise, as long as properly installed. The very fact that fiberglass is in use as an insulation material since the 1930s, without reported health problems, supports this position.

Be careful, anyway. Direct contact with fiberglass materials (or exposure to airborne fiberglass dust) may indeed irritate the skin, eyes, nose and throat, cause itching, which ultimately can be cause of lung cancer: installation should be properly done, to avoid unwanted exposure; fiberglass insulation packages display cancer warning labels in many countries and governmental institutions (the U.S. Occupational Safety and Health Administration (OSHA), the International Agency for Research on Cancer (IARC) and the National Toxicology Program (NTP)).