Rock Wool and Mineral Wool: Non-Combustible Thermal and Acoustic Insulation
Updated: 7 min readBy the Azl technical team
Contents
What Is Rock Wool, What Is It Made Of and How Does It Work?
Rock wool is a type of mineral wool, made by melting volcanic rock such as diabase together with a share of recycled material, spinning the melt into fine fibres, binding them and forming slabs, rolls or pipe sections. Glass wool is another mineral wool made from glass, differing in density and heat resistance, so each product is compared on its own data sheet.
It insulates thermally because the fibres trap air in small pores, reducing heat transfer by conduction and convection. It works acoustically because its open porous structure and non-directional fibres absorb sound energy within cavities, as ROCKWOOL literature explains. Its fire resistance comes from its rock origin: the material does not ignite and remains stable at temperatures above 1000°C.
- Slabs: for walls, partitions, suspended ceilings and facades, in various densities.
- Rolls: for large areas in ceilings and metal buildings.
- Pipe sections and industrial products: for hot pipes and equipment in factories.
- High-density slabs: for roofs, load-bearing applications and fire barriers.
Recommended Uses: Where It Fits and Where It Does Not
| Area | Where it fits | Where it does not |
|---|---|---|
| Walls and partitions | Double-wall cavities and drywall partitions for combined thermal and acoustic insulation | Cavities exposed to rainwater ingress without facade repairs |
| Suspended ceilings | Above suspended ceiling tiles in offices and halls to improve acoustics | Above a suspended ceiling that cannot carry the extra weight without a load check |
| Factories and warehouses | Metal walls and roofs, and insulation of hot pipes and equipment | Permanently wet areas or cold rooms without a sealed vapour barrier |
| Fire requirements | Where the specification calls for a non-combustible material and fire barriers | A substitute for a complete, designed fire protection system |
| Roofs and floors | Roofs and floors with high-density products designed for them | Directly trafficked roofs or water tanks |
Advantages and Technical Properties
- Non-combustible and does not contribute to flame spread, which matters in public buildings and factories.
- Thermal and acoustic insulation in a single material.
- Water-repellent in most products while vapour-permeable, so it does not rot or support mould according to manufacturer literature.
- Dimensionally stable; it does not shrink or crumble over time when correctly used.
| Property | Typical value | Note |
|---|---|---|
| Reaction to fire classification | Euroclass A1 per EN 13501-1 | The highest class in the European system; A1 and A2 are considered non-combustible |
| Fibre stability at high temperature | Above 1000°C | Per ROCKWOOL literature |
| Thermal conductivity λ | About 0.034–0.040 W/m·K | Varies by product, density and thickness |
| Conductivity by density (example) | 0.037 at 40 kg/m³, and 0.034 at 80–140 kg/m³ | Thermalrock S slabs, at a mean temperature of 23°C per ASTM C518 |
| Available densities | From about 40 to 140 kg/m³ within one slab range | Lower densities for cavities; higher for roofs, industry and fire |
| Water absorption | Less than 0.04% by volume | Thermalrock S slabs per ASTM C1104 |
Disadvantages and Cautions
- Moisture reduces performance: liquid water within the fibres raises thermal conductivity. Store it dry and covered, protect it from rain on site, and never install it in a wet cavity.
- Vapour control: in air-conditioned buildings in a hot, humid climate, vapour can condense inside the wall if the vapour barrier is on the wrong side. Its position, or that of a breathable membrane, is set by analysing the wall build-up, and cold pipes need a sealed vapour barrier.
- Temporary irritation during installation: coarse fibres can cause temporary itching of the skin, eyes and throat. ROCKWOOL states its fibres meet Note Q of the EU regulation and are not suspected of being carcinogenic.
- Binder decomposition: on first heat-up of equipment above about 150°C, fumes may be released from the binder, so good ventilation and suitable respiratory protection are needed.
- Not a waterproofing layer: it is not a substitute for waterproofing on roofs or walls exposed to rain.
Standard Installation Steps and Testing
- 1
Design and product selection
Define the goal (thermal, acoustic, fire), then choose density, thickness and facing (such as aluminium foil) according to the data sheet and the requirements of the Saudi Building Code.
- 2
Receipt and storage
Check product, density and thickness against the specification, and store on raised, covered pallets away from rain.
- 3
Protective equipment
Protective gloves to EN 388, goggles to EN 166 when working above shoulder height, an FFP1 mask to EN 149 in confined or dusty spaces, and clothing that covers the skin.
- 4
Cutting and fitting
Cut with a sharp knife rather than a power saw to reduce dust, fit slabs tightly without gaps between slabs or at frames, and fix them with the specified fixings.
- 5
Vapour barrier and details
Install the vapour barrier or membrane in the correct position, tape the laps with suitable tape, and seal openings and electrical outlets.
- 6
Inspection before closing
Visually check insulation continuity, the absence of gaps or compressed areas and the thickness, and photograph it before the wall or ceiling is closed. For acoustic work, on-site performance can be measured where the specification requires it.
- 7
Clean-up and handover
Clean the site by vacuuming or damping with water spray before sweeping, bag the waste, then hand over with a written warranty whose term depends on the insulation type and surface condition.
Climate Suitability by Saudi Region
| Region | Main challenge | Practical guidance |
|---|---|---|
| Central (Riyadh, Qassim) | High heat, large industrial and metal buildings, and acoustic needs in offices | Very well suited to metal walls and roofs and partitions. See sound insulation in Riyadh and thermal insulation in Riyadh. |
| Coastal (Jeddah, Dammam, Jubail) | High humidity and condensation risk in air-conditioned buildings | Careful vapour-barrier design, moisture-resistant facings and protection during storage. See wall insulation in Jeddah and thermal insulation in Dammam. |
| Southern highlands (Abha, Khamis Mushait, Al-Baha) | Cold winters and seasonal rain | Useful for reducing winter heat loss, with external walls protected from rain. See wall insulation in Abha. |
Estimated Cost
Rock wool insulation falls within the thermal insulation range of typically SAR 25 to 50 per square metre, excluding VAT. Prices are indicative and are confirmed after inspection. Sound insulation systems vary widely depending on the partitions, ceilings and accompanying layers and are priced after inspection. The main factors are density and thickness, facing type, working height and access, and the need for a vapour barrier or drywall work.
Frequently asked questions
What is the difference between rock wool and glass wool?
Both are mineral wools that insulate heat and sound. Rock wool is made from volcanic rock, withstands temperatures above 1000°C according to ROCKWOOL literature and comes in high densities for roofs, industry and fire applications. Glass wool is made from glass and is often lighter and less tolerant of very high temperatures. An accurate comparison uses the data sheets of the two proposed products.
Is rock wool really fire resistant?
ROCKWOOL stone wool products are classified Euroclass A1 under EN 13501-1, the highest class for non-combustible materials, and their fibres remain stable above 1000°C. However, the fire resistance of a wall or ceiling in minutes depends on the complete tested system, not the material alone, so the details of the approved system must be followed.
What density is right for acoustic insulation in partitions?
Partitions and suspended ceilings usually use low- to medium-density slabs that fill the cavity tightly, while higher densities are used for roofs, industrial applications and fire resistance. Acoustic performance also depends on the number of drywall layers, frame isolation and sealing of openings, so the product is chosen as part of the partition design, not in isolation.
Is rock wool harmful to health during installation?
It can cause temporary itching of the skin, eyes and throat. ROCKWOOL recommends gloves, goggles when working above shoulder height, an FFP1 mask in confined spaces and covering the skin, and states its fibres meet Note Q of the EU regulation and are not suspected of being carcinogenic. Clean up by vacuuming, not dry sweeping.
What happens if rock wool gets wet?
Most products are water-repellent, but water that gets between the fibres raises thermal conductivity and reduces insulation until it dries. Repeated or continuous wetting can harm surrounding materials and fixings. So it is stored covered, never installed in a wet cavity, and the moisture source is fixed before installation, with a correctly designed vapour barrier.
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References and sources
- Thermalrock S Technical Datasheet — ROCKWOOL · rockwool.com
- Product Application Guide (product capabilities factsheet) — ROCKWOOL · rockwool.com
- Euroclass System of Products Fire Classification — ROCKWOOL UK · rockwool.com
- Safe Use Instruction Sheet: ROCKWOOL stone wool insulation — ROCKWOOL UK · rockwool.com
External links pass through Azl's Consumer Safety Center for checking before leading to other organisations' websites. Citing them does not imply they endorse Azl. Technical values are typical and vary by product; the final reference is the approved product's datasheet and the project design. Editorial policy