Abstract: Mineral wool capable of dissolving in a physiological medium, which mineral wool comprises the constituents below in the following percentages by weight: SiO2 39-55%, preferably 40-52% Al2O3 16-27%, ″ 16-25% CaO  3-35%, ″ 10-25% MgO  0-15%, ″  0-10% Na2O  0-15%, ″  6-12% K2O  0-15%, ″  3-12% R2O (Na2O + K2O) 10-17%, ″ 12-17% P2O5 0-3%, ″ 0-2% Fe2O3  0-15%, B2O3 0-8%, ″ 0-4% TiO2 0-3%, and in that MgO is between 0 and 5%, especially between 0 and 2%, when R2O≦13.0%.

Abstract: The subject of the invention is a mineral wool composition capable of dissolving in a physiological medium which comprises the constituents below, having to the following percentages by weight:______________________________________ (CaO + MgO + BaO + Na.sub.2 O + K.sub.2 O + B.sub.2 O.sub.3) > 30* 2 .times. Al.sub.2 O.sub.3 RO 13.5 to 19.5% R.sub.2 O 14.2 to 23% RO/R.sub.2 O 0.70 to 0.95 CaO/MgO > 1.5 SiO.sub.2 47 to 58.5% Al.sub.2 O.sub.3 0 to 3.5% B.sub.2 O.sub.3 5 to 10% Fe.sub.2 O.sub.3 (total iron) 0 to 3.0% ______________________________________where:RO means oxides of the elements from column 2a of the Periodic Table, including CaO, MgO, BaO and SrO; and R.sub.2 O means oxides from column 1a of the Periodic Table, including Na.sub.2 O, K.sub.2 O and Li.sub.2 O.

Abstract: The invention relates to "two-component" inorganic fibers obtained by conjoint fiber formation from two different inorganic compositions, especially two glass compositions based on SiO.sub.2, alkali metal oxides and alkaline-earth metal oxides;the two inorganic compositions have thermal expansion coefficients .alpha. exhibiting a difference .DELTA..alpha. of at least 20.times.10.sup.7 K.sup.-1,they have a minimum viscosity temperature of fiber formation T.sub.log3 of between 830 and 1010.degree. C.,they exhibit a work range of at least 30.degree. C.,each includes, as weight percentages, in all less than 3% of the following compounds: TiO.sub.2, ZnO, BaO and Li.sub.2 O and preferably less than 1% of each of these,they exhibit, as weight percentages, differences in respective contents of boron oxides B.sub.2 O.sub.3 and of sodium oxide Na.sub.2 O such that:(i) .DELTA.B.sub.2 O.sub.3 >2%(ii) .DELTA.Na.sub.2 O>2%.