Polymeric film and method of making same

A polymeric film having an orthogonal length and width, the polymeric film comprising:

• a substrate;
• and
• a plurality of fins extending along the length and arranged across the width, the plurality of fins being substantially coextensive with the substrate along the length, the substrate having an average thickness T in a direction orthogonal to the length and width, the fins extending from the substrate to an average height H along a height direction and having an average width W at tips of the fins along a direction orthogonal to the height direction, wherein H/W>40 and H/T≥40, each fin in at least a majority of the fins comprises:
• a first portion extending from the substrate to a tip of the fin opposite the substrate;
• and
• a second portion extending from the tip of the fin toward or to the substrate, the second portion attached to the first portion proximate the tip, the first and second portions having different respective first and second compositions, the second portion and the substrate having surface tensions differing from one another by at least 10%.