An absorbent structure expands to a greater extent along one surface than along an opposite surface when in the presence of a liquid. The absorbent structure may include a single layer, or two or more layers intimately bonded to one another. When in the presence of a liquid, the more expandable surface...http://www.google.es/patents/US7799967?utm_source=gb-gplus-sharePatente US7799967 - Differentially expanding absorbent structure
