A polymeric film has an orthogonal length and width. The polymeric film includes a substrate and a plurality of fins extending away from the substrate and substantially coextensive with the substrate along the length. The fins are arranged across the width. Each fin in at least a majority of the fins includes 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 is attached to the first portion proximate the tip and separated from the first portion proximate the substrate along at least a portion of the length. The first and second portions have different respective first and second compositions.