A structured film of a semi-crystalline polyolefin and a beta-nucleating agent is disclosed. The structured film has a backing and upstanding posts attached to the backing. At least a portion of the film typically includes beta-spherulites. In some embodiments, the backing is microporous while the upstanding posts have lower porosity. A method of making a structured film is also disclosed. The method includes extruding a melt of a polyolefin and a beta-nucleating agent in the presence of a tool to provide the structured film having upstanding posts on a backing and cooling at least a portion of the structured film to a temperature sufficient to form beta-spherulites. In some embodiments, the method further includes stretching the structured film containing beta-spherulites to provide micropores in the backing.
