A convex shell for use in a base plate of an ostomy appliance includes an annular ring defined by an outer edge and an inner edge of defining a through-going hole. The annular ring has at least four transition sections extending transversely across the annular ring, dividing the annular ring into at least a first, second, third and fourth segment. By changing the characteristics of the convex shell in such sections, it is possible to control the bending of the shell. The shell also makes it possible to keep the area around the stoma more stable and resistant towards collapsing, while providing improved flexibility in the peristomal area for better comfort.