Mineral wool insulation was once the most commonly used type of insulation, until it began to be replaced by fiberglass insulation about thirty to forty years ago. Mineral wool is making a comeback in many newer homes because of the ease of its production. This type of insulation actually comes in two types: rock wool and slag wool.
Rock Wool vs. Slag Wool
Rock wool accounts for only 20% of mineral wool, and it is produced from crushed natural rock. Slag wool makes up the other 80% of mineral wool insulation; it is manufactured from an industrial waste by-product known as iron ore blast furnace slag. This by-product is derived from limestone, combined with various other chemicals and spun under high heat into strong fibrous materials. The main characteristic of both rock wool and mineral wool is that they both are made from about 75% recycled materials.
Rock and slag wool contain recycled materials, such as cotton and cellulose. Recycled cotton entails mixing both cotton and polyester mill fabric scraps with plastic fibers, and combining them through high heat processes. During this manufacturing process, fire-retardant chemicals and binding agents are added as well. An advantage of mineral wool is that it will not retain moisture and therefore will not develop mold or mildew. Recycled cellulose used in mineral wool insulation is mostly derived from post-consumer recycled newspaper scraps. The only drawback about mineral wool that uses recycled cellulose is the loss of fire-retardant chemicals which are not compatible with the rest of the fibers.
Mineral Wool Considerations
No matter which type of mineral wool you decide to use for your insulation needs, there are a few things to keep in mind. Check the amount of loose fill fiber, since too much of this can get knocked out of place by high winds; it can also accumulate dust and dirt over longer periods of time. Some mineral wool insulation can also be prone to wood-boring insects in certain areas of the country. Be sure to select a type of mineral wool insulation that is durable enough to withstand these possible problems and prevent frequent replacement.
Mineral wool also has an advantage of acting as a vapor barrier, as opposed to fiberglass insulation that needs to have a separate vapor barrier installed at the same time. This feature makes mineral wool more convenient to install and effective against moisture. A downside to mineral wool is that it has the same health concerns as fiberglass, so protection of the skin, eyes, and lungs is mandatory when performing this insulation.
R-value and Thickness
Mineral wool insulation can come in different thicknesses and R-values, which measure the rates of heat flow and retention. If you have mineral wool insulation that only comes in lower R-values, try to select one which has thicker fibers. The main measure you can take against energy loss is to have your home well insulated with higher quality mineral wool panels.