What mineral wool actually is
Mineral wool is a collective term for fibrous insulation made by melting and spinning inorganic raw materials. The two commercially dominant types are glass wool (glasswool), made from recycled glass, and stone wool (rock wool), made primarily from basalt or diabase. Both consist of tangled fine fibres that trap air and dissipate sound energy — the same mechanism that gives them thermal insulation properties, though the density ranges needed for acoustic performance differ from those optimised for heat.
In the Czech Republic, mineral wool products are produced and distributed under several brand families. All significant products carry CE marking and must meet declared performance values under EN 13162 (thermal and acoustic properties for building applications).
Glass wool versus stone wool: the core differences
Glass wool fibres are thinner and more flexible, making the material easier to compress and cut. It works well in partitions, suspended ceilings, and lightweight metal-stud constructions where the insulation does not bear load. Its acoustic absorption coefficient (αw) is high in the mid-frequency range — around 0.95 for 50 mm at 500 Hz in many products — but it loses performance at low frequencies unless greater thickness is used.
Stone wool is denser and stiffer. Densities used for acoustic purposes typically run between 40 kg/m³ and 150 kg/m³, compared to 10–32 kg/m³ for thermal glass wool. Higher-density stone wool boards (60–100 kg/m³) are used under floating floors to reduce impact sound transmission, and they provide the mechanical resistance needed to prevent the floor system from bottoming out under load.
| Property | Glass wool (acoustic) | Stone wool (acoustic) |
|---|---|---|
| Typical density range | 15 – 32 kg/m³ | 40 – 150 kg/m³ |
| Primary acoustic use | Partitions, ceilings | Floating floors, heavy walls |
| Sound absorption (αw, 50 mm) | 0.85 – 0.95 | 0.70 – 0.90 |
| Compressive strength | Low | Medium to high |
| Moisture resistance | Moderate | Good |
| Reaction to fire class | A1 or A2 | A1 |
Density and its effect on sound reduction
A common misconception is that denser insulation is always better for sound. For airborne sound, the relationship between density and performance is not linear. A glass wool batt at 32 kg/m³ in a correctly sealed and resilient partition can outperform a stone wool board at 60 kg/m³ that is incorrectly fitted. What matters is the complete assembly — the insulation fills the cavity and reduces resonance, but the overall weighted sound reduction index (Rw) of the partition depends equally on the mass of the flanking layers and whether sound bridges have been eliminated.
For impact sound under floating floors, higher density matters more. The dynamic stiffness (s') of the underlayer determines the natural frequency of the floating system. Products with a declared s' value are tested to EN 29052-1. The lower the s' value (measured in MN/m³), the more effective the layer is at reducing low-frequency impact transmission. Stone wool boards designed for this use typically carry s' values in the range of 5–25 MN/m³.
Formats available in the Czech market
Czech builders' merchants and specialist suppliers stock mineral wool in several formats. Rolls are the most economical for infilling stud-frame partitions and are available in widths matched to standard stud spacing (600 mm). Rigid boards are used where compressive strength is needed — under screed floors and in ventilated facades. Semi-rigid batts occupy a middle ground and are favoured for ceiling systems where the material must hold its position against gravity without mechanical fastening.
Loose-fill mineral wool, blown into cavities, is used in renovation projects where access is limited, but its acoustic performance is less predictable than cut-and-fit products and it requires specialist equipment.
Handling and health notes
Mineral wool fibres can cause skin and respiratory irritation during cutting and installation. Current products — both glass wool and stone wool — use biopersistent-fibre-free formulations that have been classified as non-carcinogenic under European regulations. Gloves, long sleeves, and a suitable dust mask (P2 or better) remain recommended for any cutting work. The fibres settle quickly and standard ventilation is sufficient to clear the air after work is complete.
Further reading
Performance data for specific products is available from manufacturer technical departments. The acoustic properties of mineral wool assemblies are also summarised in TZB-info.cz, a Czech technical portal that publishes regularly updated construction detail sheets.