SUR FIT Natura Two Piece High Output Pouch. The SUR-FIT Natura Two-Piece Ostomy System is ConvaTec?s most extensive two-piece product line. The SUR-FIT 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. The High Output pouches come with a removable filter that reduces pouch ballooning and neutralizes odor, an anti-reflux valve that decreases liquid output backflow, and an outlet with spout and cap that quickly and easily drains high liquid output.