In the manufacture of electronic devices that use porous dielectric materials, the properties of the dielectric in a pristine state can be altered by various processing steps. In a method for restoring and preserving the pristine properties of a porous dielectric layer, a substrate is provided with a layer of processed porous dielectric on top, whereby the processed porous dielectric is at least partially exposed. A thin aqueous film is formed at least on the exposed parts of the processed porous dielectric. The exposed porous dielectric with the aqueous film is exposed to an ambient containing a mixture comprising at least one silylation agent and dense CO2, resulting in the restoration and preservation of the pristine properties of the porous dielectric.