Abstract: A fine-grained kaolinite-illite clay, in which planar particle orientation resulted from filtration or plastic deformation, swelled differentially when liquid water was imbibed by test pieces already in the plastic state. Swelling was greater perpendicular than parallel to the plane in which the clay platelets tended to be arranged. Filtration, in contrast to deformation, gave test pieces that swelled more rapidly and extensively. The slipbands, present only in plastically deformed test pieces, restricted the swelling. They were arranged diagonally to the plane in which the clay platelets tended to lie. The plastically deformed test pieces showed enhanced expansion perpendicular to this plane when they were made successively thinner by compression under a cylindrical roller. This was attributed to improved planar orientation of the clay platelets.