Abstract: Microporous materials and articles are disclosed. The microporous materials contain a polyolefin or olefinic polymer and a solid diluent in which the polymer is soluble at a temperature above the melting temperature of the polymer and that phase separates from the polymer at a temperature below the polymer crystallization temperature. The resulting material is a microporous material having a polymeric matrix with solid diluent present throughout. The invention is also directed to methods of forming the microporous material using thermally induced phase separation and subsequent processing.