The synthesis of silica-fume based foams, with a multi-range macroporosity, was obtained by alkaline activation. Foams were obtained through an in situ foaming process exploiting the gaseous production of hydrogen caused by the oxidation, in alkaline medium, of metal silicon impurities contained in silica fume. Potassium or sodium alkaline solutions were selected and a temperature of 70 degrees C was sufficient to promote the development of hydrogen bubbles, the increase of the viscosity and the consolidation of the foams. The balance of these reactions allowed to entrap hydrogen bubbles inside the structures creating highly porous foams. The foams were characterized in term of macro- and microstructure, porosity distribution, infrared spectroscopy, thermal and acoustic properties achieved. The foams showed ultramacroporous structures, with a total porosity of approximate to 80%. The average values of bulk density (0.5 g cm(-3)), thermal conductivity (0.16 Wm(-1) K-1), and the acoustic behaviors, highlighted a use of the foams as promising insulating materials. (C) 2016 Elsevier B.V. All rights reserved.