Reaction to fire: both non-combustible, separated by temperature
Both rock wool and glass wool are non-combustible mineral wools. Taishi® rock wool is declared Euroclass A1 for reaction to fire under EN 13501-1, as stated on our CE certificate to EN 13162 (Intertek NB 2649); it does not ignite, adds no fuel to a fire and releases no significant smoke. Glass wool, as a class, is also inorganic and generally reaches Euroclass A1 or A2-s1,d0 under the same standard. On the reaction-to-fire class alone the two are broadly comparable. The decisive fire distinction is not the class but how each behaves as temperature rises, which the fibre's melting and softening point sets. That is the next property.
Temperature endurance: rock wool holds integrity far hotter
This is where the two materials genuinely diverge. Taishi® rock wool is spun from basalt-type rock and has a melting point above 1,000°C (above 1,150°C on the fireproof black grade) and a maximum continuous service temperature up to about 650°C on high-density boards. That lets a single fire barrier or industrial jacket keep its shape and insulating function through a prolonged, high-temperature fire. Glass wool, as a class, is spun from recycled glass and sand and softens at a markedly lower temperature, typically around 600°C; above that its fibre structure begins to slump and lose integrity. For passive fire protection, firestops and high-temperature process insulation, the higher melting point is the reason rock wool is specified.
Thermal conductivity: glass wool marginally lower per kilogram
For everyday thermal insulation the two are close. Taishi® rock wool lists thermal conductivity limits of 0.038 to 0.050 W/(m·K) across the range, from ≤0.038–0.040 W/(m·K) on standard building boards to ≤0.050 W/(m·K) on the densest marine grades, and lab measurements to EN 12667 fall within these limits. Glass wool, as a class, commonly reports a marginally lower value of around 0.030 to 0.040 W/(m·K) at low density, which is one reason it is popular in lightweight, cost-led building envelopes. The gap is small and narrows once temperature, moisture or load enter the picture, because rock wool holds its stated value across a wider service range where glass wool is compressed or heated.
Density and strength: rock wool carries load, glass wool does not
Taishi® rock wool is manufactured across a broad density band, from about 40 to 220 kg/m³, and that density buys mechanical strength. Compressive resistance is declared per grade: at least 40 kPa on standard wall and roof boards, at least 80 kPa on the densest roof board, and up to 200 kPa (EN 826) on the highest-density marine grade. Roof boards also carry point loads of ≥200 to ≥700 N. This is what lets rock wool sit under a loaded roof deck, behind a rendered façade, or as a structural sandwich-panel core. Glass wool, as a class, is a lighter, lower-density product usually supplied as soft rolls or semi-rigid batts; it offers limited compressive resistance and is not normally specified where the insulation itself must carry load or resist foot traffic.
Acoustics: both absorb sound, rock wool leads at low frequency
Both materials are open, porous fibre and absorb airborne sound well. Taishi® multipurpose rock wool board reaches a noise reduction coefficient above 0.45, and its higher-density grades improve absorption at low frequencies and add mass to a partition, which raises airborne sound insulation. Glass wool, as a class, is also an effective absorber and performs particularly well at mid-to-high frequencies thanks to its light, open structure. Its lower density generally makes it less effective than high-density rock wool at low frequencies and in dense partition or floating-floor build-ups. Where the target is a heavy, low-frequency-rated partition or a machine enclosure, density favours rock wool; for light mid-to-high lining, glass wool is often sufficient.
Water and durability: density and treatment favour rock wool
Taishi® rock wool is hydrophobic-treated to a water-repellency rate above 98 to 99% by series, with low moisture absorption and dimensional stability within 1.0%. It is inorganic, rot-proof, does not feed mould, and holds its thermal performance for decades in humid, coastal or marine service. The marine boards carry a CCS works approval for shipbuilding. Glass wool, as a class, can also be supplied water-repellent-treated, but being a lighter product it is generally more compressible and more sensitive to moisture over a long service life, particularly where it is not kept dry. Both are inorganic and non-combustible; the durability gap is one of density and water handling, not of chemistry.