Micro-porous sheet

A micro-porous sheet comprising a cellulose ester as a basic component and about 0.1 to 20 wt% of a cellulose ether based on the cellulose ester wherein said cellulose ester is cellulose diacetate, cellulose triacetate, nitrocellulose, cellulose acetate butyrate, cellulose propionate or a mixture thereof and said cellulose ether has the formula ##STR4## wherein n is the degree of polymerization, and R is --H, --CH.sub.3, or --CH.sub.2 CH.sub.3, with the average degree of substitution where R is --CH.sub.3 or --CH.sub.2 CH.sub.3 ranging from about 1.0 to 1.9 and where a portion of the --CH.sub.3 and --CH.sub.2 CH.sub.3 groups can be replaced by a member selected from the group consisting of --CH.sub.2 CH.sub.2 OH, --CH.sub.2 CH.sub.2 CH.sub.2 OH, --CH.sub.2 CH.sub.2 OOCCH.sub.3, --CH.sub.2 CH.sub.2 CH.sub.2 OOCCH.sub.3, ##STR5## such that the average degree of substitution by said member ranges from 0 to about 0.3 and wherein the average pore size of the microporous sheet is less than 10 microns.