A collecting bag configured to collect stomal fluids from a stoma of a user comprising: first and second exterior bag walls (24, 26) attached to each other along a peripheral attachment zone and defining a longitudinal direction of the bag between a top enc portion of the bag and a bottom end portion of the bag, one of the first and second exterior bag walls comprising an inlet opening at the top end portion of the bag, wherein a collecting volume of the bag is formed between the exterior bag walls; a drainage outlet provided at the bottom end portion of the bag and attached to one or both bag walls, configured to allow drainage of collected stomal fluids; and an anti-reflux component attached to the bag and configured to prevent reflux of collected stomal fluids from the collecting volume to the inlet opening, wherein the anti-reflux component comprises an interior, proximal contoured sheet comprising a receiving opening communicating with the inlet opening, and ar interior, distal contoured sheet; the interior contoured sheets of the anti-reflux component being connected to each other such as to define at least one passage between them towards the collecting volume, the at least one passage having a width in a direction transverse to the longitudinal direction, and to define two or more non-linear connection zones (58a, 58b) extending generally in the longitudinal directior from the at least one passage to the top end portion of the bag; characterised in that the interior contoured sheets of the anti-reflux component combine to define two passage (56a, 56b) provided in a side-by-side relationship with each other in the transverse direction separated by a center connection zone, in which the interior contoured sheets of the anti-reflux component are connected to each other, and wherein the center connection zone is configured to have a greatest extent transverse to the longitudinal direction at a bottom edge of the anti-reflux component and to gradually decrease in transverse extent towards the top end portion of the bag. first and second exterior bag walls (24, 26) attached to each other along a peripheral attachment zone and defining a longitudinal direction of the bag between a top enc portion of the bag and a bottom end portion of the bag, one of the first and second exterior bag walls comprising an inlet opening at the top end portion of the bag, wherein a collecting volume of the bag is formed between the exterior bag walls; a drainage outlet provided at the bottom end portion of the bag and attached to one or both bag walls, configured to allow drainage of collected stomal fluids; and an anti-reflux component attached to the bag and configured to prevent reflux of collected stomal fluids from the collecting volume to the inlet opening, wherein the anti-reflux component comprises an interior, proximal contoured sheet comprising a receiving opening communicating with the inlet opening, and ar interior, distal contoured sheet; the interior contoured sheets of the anti-reflux component being connected to each other such as to define at least one passage between them towards the collecting volume, the at least one passage having a width in a direction transverse to the longitudinal direction, and to define two or more non-linear connection zones (58a, 58b) extending generally in the longitudinal directior from the at least one passage to the top end portion of the bag; characterised in that the interior contoured sheets of the anti-reflux component combine to define two passage (56a, 56b) provided in a side-by-side relationship with each other in the transverse direction separated by a center connection zone, in which the interior contoured sheets of the anti-reflux component are connected to each other, and wherein the center connection zone is configured to have a greatest extent transverse to the longitudinal direction at a bottom edge of the anti-reflux component and to gradually decrease in transverse extent towards the top end portion of the bag.