Convatec Natura + Drainable Pouch. Pouches are compatible with SUR-FIT Natura Two-Piece Ostomy System which is ConvaTecs most extensive two-piece product line. The SUR-FIT Natura and Natura + Flange System signals a secure, accurate closure with a series of audible clicks. A simple snap-off, snap on design allows users to change the pouch quickly to match activities without removing the skin barrier from the skin.