Patent ID: 8906815

Claim:
A composite nonwoven fibrous web comprising: a population of sub-micrometer fibers having a median diameter less than one micrometer (μm); and a population of meltblown microfibers having a median diameter of at least 1 μm, wherein at least one of the fiber populations is oriented, and further wherein the composite nonwoven fibrous web is formed as a single layer having a thickness and exhibiting a Solidity of less than 10%, wherein the population of sub-micrometer fibers is intermixed with the population of microfibers to form an inhomogeneous mixture of fibers wherein a ratio of the number of sub-micrometer fibers to the number of microfibers varies from a peak value proximate a centerline defined by the half-thickness of the composite nonwoven fibrous web, to a lower value at a major surface of the composite nonwoven fibrous web.