Enclosure and an infant playpen including the same

An enclosure for an infant playpen includes a flexible material installable on a support frame of the infant playpen, the flexible material including at least one pleat comprised of two folds 152 that are folded toward each other over a base region 154 of the flexible material and respectively have two folded edge portions 152A adjacent to each other, each of the two folded edge portions having at least one end affixed to the flexible material. Optionally the enclosure has a sidewall including an inner and outer layer with a hollow interior between them and includes an opening communicating with the hollow interior. Also disclosed is an infant playpen comprising a support frame and the enclosure, wherein the pleat is located adjacent to a pivot connection of the support frame when the enclosure is installed on the support frame.