Type of plastic sheeting to use for shelter-in place?

DHS recommends using plastic sheeting with a thickness of 4 to 6 mil (0.004 in - 0.006.) or greater. For reference, commercially available sheeting is typically sold at 0.7, 1, 1.2, 1.5, 2, 2.5, 3, 4, 6, and 10 mil.