A method of depositing a conformal coating on a porous non-ceramic substrate requires reactive gases to flow through the substrate so as to leave a conformal coating behind. The process can be used to leave a hydrophilic surface on the interior pores of the substrate, even when the substrate is of a naturally hydrophobic, e.g., olefinic material. The method can be used in a roll-to-roll process, or in a batch process. In some convenient embodiments of the latter case, the batch reactor and the conformally coated substrate or substrates can together go on to be come part of the end product, e.g., a filter body and the filter elements respectively.