1-piece systems
The skin barrier and pouch are a single unit, applied and removed together. This tends to be lower-profile and more flexible against the body, which some people find more comfortable, but the whole system is discarded when changed.
2-piece systems
The skin barrier stays in place while the pouch clicks or locks on separately, so the pouch can be changed without removing the barrier from the skin — useful for people who want to change pouches more often than they change the barrier, or who want to rotate pouch styles.
Convex vs. flat barriers
Convex barriers curve outward to help the stoma protrude further, which can improve the seal for stomas that are flush or recessed, or for skin with folds/creases around the stoma. Flat barriers suit stomas that protrude well on their own.
Getting the right fit
We carry major brands (Coloplast, Hollister) in multiple configurations, and can help you work through fit and skin-barrier issues rather than guessing on your own.