Glasswool or Rockwool

Glasswool (Fiberglass)

Glass wool is made from a mixture of natural and recycled glass (recycled bottles, car windscreens and window panes) which is melted at 1,450 °C, where the glass that is produced is converted into fibers. It is typically produced in a method similar to making, forced through a fine mesh by and cooling on contact with the air. The cohesion and mechanical strength of the product is obtained by the presence of a that “cements” the fibers together. Ideally, a drop of binder is placed at each fiber intersection. This fiber mat is then heated to around 200 °C to resin to give it strength and stability. The final stage involves cutting the wool and packing it in rolls or panels (referred to as slabs or batts). Contrary to popular belief that mineral wool properties are defined solely by density, different fibre diameters, lengths, binder contents, additives, cutting and packaging can give a diverse product range.

Rockwool (Stone wool, Slag wool)

Stonewool is made from volcanic rock (dolomite, diabase and basalt), which is not a recycled material, but is an abundant resource. Slag wool is made from the recycled waste product of a blast furnace. Stonewool gives a higher quality and performing product than Slag wool, even though the two are often referred to as Rockwool. Like glass wool, the volcanic rock is heated to about 1,500°C, which causes it to melt. The liquid volcanic rock is then spun at high speeds to produce rock fibres, which is then bound together with the same resin used in glass mineral wool and small amounts of oil to reduce dust, creating the mineral wool.

These three mineral wool materials have similar properties.

  1. They are all A1 non-combustible and will not burn in a building fire.
  2. Thermally, they work on the principal of trapping air in small cells which cannot effectively transfer heat by natural convection. Convection involves a larger bulk flow of gas driven by buoyancy and temperature differences, and it does not work well in small cells where there is little density difference to drive it. The same principle used in mineral wool is used in other man-made insulators such as wet suit neoprene foam fabrics, and fabrics such as Gore-Tex and polar fleece. The air-trapping property is also the insulation principle used in nature in down feathers, and insulating hair such as natural wool and even the hair on one’s head.
  3. Acoustically, they provide excellent noise reduction by forming the spring in mass-spring-mass partition systems acting like the suspension system in your car and, due to the fiberous nature of the wool, higher frequency noise is also defused by reflecting sound waves in a variety of directions and consequently minimizing the sound either directly transmitted or reflected. In effect, this is the principal applied by having egg boxes on the walls of amateur recording studios.

Is glass wool better thank rock wool?

Why not ask the people who make both? There has been much debate over the merits of rock mineral wool compared to glass mineral wool insulation. In the developing part of the world, there is also a lot of mis-information around the two materials. The simple answer is that the best material is dependent on the application and specific performance requirements. As a major manufacturer of both glass and rock mineral wool insulation solutions, Knauf Insulation is able to offer impartial advice. Trust in the experience and expertise of Knauf Insulation to guide you towards the most appropriate solution.

Comparative Performance

Thermal Performance (Glass)

Where thermal performance is the primary requirement of the insulation material, then glass mineral wool offers a much more versatile and cost effective range at lower weights. Glass wool can achieve best lambda values of 0.31 as oppose to 0.35 for Rockwool, more than 10% more thermally efficient. This means that the material can be 10% thinner for a like for like performance. More importantly, it can achieve this performance at less than half the weight. For example, Knauf Insulation in the UAE is capable of a 0.32 lambda product at 36kg density, compared to a best rock performance of 0.35 at c. 80-100kg density. Although kg by kg, glass is more expensive, for an equivalent thermal performance, glass is the most cost effective solution. Therefore, glass has become the preferred insulation in the developed world for facade cladding, cavity, steel structures, HVAC and above ceiling insulation.

Acoustic Performance (Glass other than where compressive strength is required)

In acoustic applications there is negligible difference between rock and glass wool in terms of optimal performance other than glass wool typically achieves the same db reduction with less than half the mass. A deciding factor can sometimes be the secondary feature of a product. For example, glass wool can also give far higher thermal performances, which may also help to retain heat in certain zones when partitioning between rooms in domestic housing. Glass wool is also often considered easier to handle due to its weight and longer, less itchy and dusty, fibers. For this reason, acoustic glass roll products now dominate the partition wall sector. Where there can be direct contact with the material after installation, such as internal wall linings, compressive strength can be a key deciding factor. Although both materials have similar compressive strengths at the same density, rock is cheaper on a kg to kg basis. For this reason, rock mineral wool can lend itself to be the most competitive solution.

Compressive Strength (Rock)

Compressive strength is required where a construction may be put under high weight loading. Not only can rock be made up to 200kg in density (compared to glass at c.110kg), it can also give a more cost effective performance where compressive strength is the primary requirement. The typical application where compressive strength is required is flat roof.

Fire Protection (Rock)

A common misconception in the market is that Glass burns and Rock doesn’t. This is not correct! Both products are A1 non-combustible and will not burn or contribute to a building fire.It is also a common misconception that all Rock mineral wool will stop fire. The simple fact is that a high density mineral wool product (120kg m3) is required to stop fire. At these densities, rock mineral wool is the most cost effective solution and provides excellent fire protection to prevent structural collapse in the event of a fire and to allow human occupants to safely exit the building. However, like glass mineral wool, low density rock mineral wool insulation will not burn, but will also not stop flames from penetrating between the fibres. In short, for fire protection between floors in the facade of a building and for major steel supports, high density Rock mineral wool is the ideal solution.

High Temperature Applications (Rock)

Maximum service temperature is a measure indicating the maximum continous temperature at which an insulation material can operate without any loss in thermal insulation performance. A common misunderstanding is that this is the maximum temperature before the product burns. This is not the case, all mineral wool is A1 non-combustible. However, rock mineral wool is able to tolerate higher temperatures without any loss to its insulation properties than glass mineral wool. Typically, glass mineral wool can operate up to 400°C (typically 230°C without modification) whereas rock can operate up to 700°C. For this reason, in high temperature process plants, rock mineral wool is the most commonly found insulation type.

Recovery from Packaged Compression (Glass)

The fibre characteristics of glasswool facilitate the high compression of product without affecting recovery to the required thickness after unpacking, resulting in high transport and storage efficiencies (e.g. 4385m2 of 100mm FactoryClad product on a HGV, 277% more than the rock wool equivalent). The characteristics of rock wool do not allow the product to be highly compressed in packaging, resulting in comparatively inefficient transportation and storage (e.g. 1584m2 of 100mm roll product on a HGV).

Water Resistance (Glass or Rock are good)

It is a common misconception that glass or rock mineral wool fibres are damaged by water. This is not the case. However, water can occupy the cells between the fibres, replacing the insulating pockets of air and thus stopping the material from performing its thermal insulating requirements. The lighter the density, the easier it is for the water to penetrate. Don’t be fooled by demonstrations of one material against the other where different densities are being used with different coatings. Importantly, the water resistance of mineral wool (Glass and Rock) can be engineered to meet the conditions of their application. For instance, in Knauf’s factory clad, facade and cavity wall products, silicon is added as a water repellent stopping water from penetrating the air pockets whilst insitu in the application.

Is glass wool better thank rock wool?

Is glass wool better thank rock wool?

In conclusion, is glass wool better than rock wool? It depends on your area of business and the application you require. But with advice from Knauf Insulation, you can be assured that you will always use the most appropriate insulation for the job.