Process for producing expanded sodium silicate spherules or a manufactured article formed by said spherules, comprising the following steps: a) preparing a mixture comprising 15 to 70% by weight of a first component consisting of an acidic aqueous solution having a pH comprised between 1.0 and 2.6, and 30 to 85% by weight of a second component selected from an alkyl-trialkoxysilane and a mixture of an alkyl-trialkoxysilane and a tetraalkoxysilane, said acidic solution prepared by addition to distilled water of an acid selected from hydrochloric acid, nitric acid, chloric acid and perchloric acid; b) allowing the mixture to react for at least 8 hours at a temperature comprised between 18 and 35 °C, obtaining a sol; b') optionally, diluting the sol obtained in step b) with a C1-C6 alcohol or a mixture thereof; c) dripping into the sol, maintained under gentle stirring, an aqueous sodium silicate solution having formula (SiO 2 ) x ·(Na 2 O) y wherein the ratio x/y may vary between 1.5 and 3.9, obtaining sodium silicate spherules at the bottom of the sol container; d) removing the sol by filtration, recovering the sodium silicate spherules having the surface covered with a thin layer of sol; e) subjecting the sodium silicate spherules having the surface covered with a thin layer of sol, obtained in step d), to a thermal treatment at a temperature between 180 and 320 °C, keeping them separated, obtaining dry spherules of expanded sodium silicate; or, alternatively, f) transferring the sodium silicate spherules having the surface covered with a thin layer of sol, obtained in step d), into a closed mould having the shape of the desired final article and bringing them into the mould at a temperature comprised between 180 and 320 °C, obtaining a manufactured article. a) preparing a mixture comprising 15 to 70% by weight of a first component consisting of an acidic aqueous solution having a pH comprised between 1.0 and 2.6, and 30 to 85% by weight of a second component selected from an alkyl-trialkoxysilane and a mixture of an alkyl-trialkoxysilane and a tetraalkoxysilane, said acidic solution prepared by addition to distilled water of an acid selected from hydrochloric acid, nitric acid, chloric acid and perchloric acid; b) allowing the mixture to react for at least 8 hours at a temperature comprised between 18 and 35 °C, obtaining a sol; b') optionally, diluting the sol obtained in step b) with a C1-C6 alcohol or a mixture thereof; c) dripping into the sol, maintained under gentle stirring, an aqueous sodium silicate solution having formula (SiO 2 ) x ·(Na 2 O) y wherein the ratio x/y may vary between 1.5 and 3.9, obtaining sodium silicate spherules at the bottom of the sol container; d) removing the sol by filtration, recovering the sodium silicate spherules having the surface covered with a thin layer of sol; e) subjecting the sodium silicate spherules having the surface covered with a thin layer of sol, obtained in step d), to a thermal treatment at a temperature between 180 and 320 °C, keeping them separated, obtaining dry spherules of expanded sodium silicate; or, alternatively, f) transferring the sodium silicate spherules having the surface covered with a thin layer of sol, obtained in step d), into a closed mould having the shape of the desired final article and bringing them into the mould at a temperature comprised between 180 and 320 °C, obtaining a manufactured article. <EOS>