A stoma seal is described for a controlled evacuation ostomy appliance. The stoma seal may have a liquid-responsive property, such as hydrophobic, hydrophilic or absorptive. The stoma seal may have a non-smooth surface, e.g., at a microstructure scale. The non-smooth surface may consist of tortuous channels, protruding seals, or a confronting apertured or porous layer. The liquid-responsive property and/or the non-smooth surface may facilitate separation of flatus from faecal matter and/or facilitate venting of flatus while obstructing stool.