Method of forming blown polymeric foam film

A method of forming a blown polymeric foam film, the method comprising:

• forming a single-phase solution of polymeric material and blowing agent in an extruder;
• extruding the solution through a die by passing through an inner die passageway having an outward taper and converging in a downstream direction approaching an outlet of the die so as to form an annular polymeric foam extrudate nucleating upon said extruding;
• blowing to expand the extrudate into a blown polymeric foam film precursor;
• and
• processing the blown polymeric foam film precursor into a blown polymeric foam film, the blown film having a plurality cells having a length and thickness,
• wherein the length of the cells is greater than the thickness of the cells such that the average aspect ratio of the cell length to cell thickness is less than 3:1, the average maximum dimension of the cells being less than 150 microns, and
• wherein the blown polymeric foam film has a density between 0.05 g/cm3 and 0.90 g/cm3.