Abstract: A flexible, distensible mold for use in fabricating art forms and utilitarian articles, and for use with the aid of air pressure differential enlargement of the shaping cavity, is provided with closeable slits extending from at least a portion of the shaping cavity partly into the mold wall, and cooperating slits extending from the outer wall of the mold into a position which is adjacent to and overlapping the internal slits. With these improved molds a withdrawal bore of the shaping cavity can be greatly enlarged and the side walls can be greatly extended with lower air pressure differentials than would be otherwise necessary. This invention provides a hinging action in the expansion of the side wall which utilizes the flexibility of the mold material to expand the withdrawal bore.