A process for the hydrophobization of a porous silica based compound involves the steps of providing a composition (I) containing a porous silica based compound, treating the composition (I) with a composition (II) containing hexamethyldisiloxane or its hydrolyzed form, and removing the treated silica based compound. The porous silica based compound obtained by the process is useful. A porous silica based compound obtained or obtainable by the process can be used for medical and pharmaceutical applications, as adsorbents, for cosmetic applications, as an additive for food, as a catalyst support, for the preparation of sensors, or for thermal insulation.