The present invention relates to a calcined medium, in particular a catalyst or a catalyst medium or an adsorbent/absorbent mass, in particular in the form of extrudates, pellets, granules or beads, the medium comprising a porous matrix comprising carbonates, clays, zeolites, oxides, or metal and/or silicon hydroxides, and the matrix incorporating hollow mineral microspheres having a different composition in a content of between 0.3 and 50% by weight, in particular between 0.5 and 15% by weight, of the matrix.