Methods, plate elements and heat/enthalpy exchangers. a) perforating an unformed plate element with defined outer dimensions in any desired area and in any desired dimension; b) covering at least one side of the unformed plate element with a thin polymer film with latent energy exchange characteristics and; c) forming the plate element into a desired shape and a pattern of corrugations and/or embossing. The operations b) and c) may be performed in a different order. For instance, when the plate element is made out of plastic, b) may be performed before c) whereas, when the plate element is made out of aluminum (or plastic), c) may be performed before b). Operations a) and/or b) and/or c) may also, in certain embodiments, be combined.