Method of making polymeric multilayer films

A method of making a polymeric multilayer film, the method comprising:

• extruding at least first and second polymeric layers into a nip to provide a polymeric multilayer film, wherein the nip comprises a first roll having a structured surface that imparts indentations through a first major surface of the polymeric multilayer film, wherein the first layer comprises a first polymer having a first melting point, wherein the second layer comprises a second polymer having a second melting point, wherein the absolute difference between the first and second melting point is at least 20° C., and wherein the first major surface of the polymeric multilayer film is a major surface of the first layer and the second major surface of the polymeric multilayer film is a major surface of the second layer;
• and
• passing the first major surface having the indentations over a chill roll while applying a heat source to a generally opposed second major surface of the polymeric multilayer film, wherein the application of heat from the heat source results in formation of openings to provide a polymeric multilayer film having first and second generally opposed major surfaces, an array of openings extending between the first and second major surfaces, and at least first and second layers, wherein the first layer comprises the first polymer, wherein the second layer comprises the second polymer, and wherein the first major surface of the polymeric multilayer film is a major surface of the first layer and the second major surface of the polymeric multilayer film is a major surface of the second layer.