One Piece, Two Piece, Flat or Convex?

A beginner’s guide to urostomy pouch systems — and why finding the right bag can make such a difference

When you wake up with a urostomy for the first time, somebody will eventually introduce you to a piece of equipment that is about to become a fairly significant part of your life.

The pouch.

Or bag.

Or appliance.

Or pouching system.

There are several names for it, which is perhaps your first warning that this isn't going to be quite as straightforward as: “Here is your urostomy bag. Off you go.”

Because there isn't really such a thing as the urostomy bag.

There are one-piece systems.

Two-piece systems.

Flat baseplates.

Convex baseplates.

Different depths of convexity.

Cut-to-fit openings.

Pre-cut openings.

Different adhesives, shapes, fabrics, taps and connectors.

And then come barrier rings, seals, adhesive removers and all the other paraphernalia that can gradually colonise a bathroom cupboard.

Welcome to the world of stoma appliances.

The good news is that all of this choice exists for a reason.

Bodies are different. Stomas are different. And the pouch that works beautifully for one person may be completely wrong for another.

First: what does a urostomy pouch actually do?

A urostomy — often an ileal conduit — creates a new route for urine to leave the body through a stoma on the abdomen.

Unlike the bladder, the stoma doesn't store urine until you decide to go to the toilet.

Urine drains into a pouch worn over the stoma, which can then be emptied through a tap or bung at the bottom.

Modern urostomy pouches are waterproof and odour-proof, with an adhesive skin barrier around the stoma. They also contain a non-return valve, designed to reduce urine flowing backwards over the stoma. Urostomy Association

And that brings us to our first big decision.

One-piece or two-piece?

These terms describe how the pouch and adhesive baseplate are put together.

One-piece systems

With a one-piece urostomy pouch, the bag and adhesive baseplate are permanently joined together.

You peel off the backing, position the opening around your stoma and stick the entire appliance to your abdomen.

When it is time for a change, everything comes off together.

The Urostomy Association says one-piece systems can typically remain in place for around one to three days, although that is only a general guide and individual routines vary. Urostomy Association

The big attraction is simplicity.

There is only one appliance to apply, and one-piece systems can feel relatively flexible and discreet because there isn't a separate coupling mechanism between the pouch and baseplate.

But changing the pouch also means removing the adhesive from your skin each time.

For some people, that's absolutely fine.

For others — particularly where the skin needs a different approach — another system may suit them better.

Two-piece systems

A two-piece system separates the pouch from the adhesive baseplate, sometimes called the flange.

The baseplate sticks around the stoma.

The pouch then attaches to it.

Depending on the particular product, the connection may use a mechanical coupling or another attachment system.

The important difference is this:

You can remove the pouch without necessarily removing the baseplate from your skin.

The Urostomy Association says a two-piece flange can typically remain on the abdomen for around three to five days, while the pouch can be changed separately.

Again, these are guidelines rather than rules. Urostomy Association

That can be useful if somebody wants to disturb the skin less frequently or prefers the flexibility of changing the pouch separately.

The trade-off is that there are two components rather than one, and some people simply prefer the feel and simplicity of a one-piece appliance.

Neither system is inherently “better”.

The useful question is:

Which works better for your body and your life?

Then things get curvy: flat versus convex.

This is probably one of the most important distinctions in pouch fitting.

Look at the adhesive surface of some pouches and it is essentially flat.

Look at another and the area surrounding the opening curves outwards towards the abdomen.

That is convexity.

Flat pouches

A flat baseplate sits relatively flat against the skin surrounding the stoma.

For a stoma that protrudes nicely from an even abdominal surface and directs urine cleanly into the pouch, this may provide an excellent seal.

But not every stoma behaves quite so obligingly.

Some sit almost level with the skin.

Some retract slightly below it.

Some sit close to a crease.

Some are surrounded by softer or uneven abdominal contours.

And bodies can change after surgery, with healing, weight change and time.

That's where convexity may enter the conversation.

Convex pouches

A convex baseplate curves towards the abdomen around the stoma.

That shape can apply pressure to the surrounding area, helping a flush or recessed stoma protrude more effectively so that urine is directed into the pouch rather than underneath the adhesive.

The Urostomy Association notes that convexity may be considered where a stoma is level with the skin or situated in a crease or fold, particularly where leakage is occurring. Urostomy Association

And leaks matter.

Urine repeatedly getting underneath the baseplate can compromise the seal and contribute to sore peristomal skin.

So sometimes what looks like:

“My bag keeps leaking.”

is actually:

“This particular shape isn't fitting my body properly.”

That distinction can be transformative.

Convexity itself isn't one universal shape either. Products can have different characteristics and depths, which is one reason it's sensible to involve a stoma care nurse when deciding whether convexity is appropriate. Urostomy Association

Cut-to-fit or pre-cut?

Now we arrive at the hole.

Every pouching system needs an opening through which the stoma sits.

And there are two broad approaches.

Cut-to-fit

A cut-to-fit pouch or baseplate comes with a starter opening which you enlarge to match your stoma.

This can be particularly useful after surgery because stomas can change size and shape while healing.

You measure the stoma, mark the appropriate size and cut the opening accordingly.

Pre-cut

Once a stoma has settled into a reasonably consistent size and shape, some people prefer a pre-cut appliance. I enjoy the ease of having a precut wafer!

The opening is already manufactured at a particular diameter.

No scissors.

No template.

No cutting a suspiciously wonky circle while wondering whether you've just ruined an expensive medical appliance.

The Urostomy Association specifically notes that pre-cut products can be helpful for people with sight or dexterity difficulties as well as simply being convenient once the stoma has stabilised. Urostomy Association

Again: one isn't intrinsically superior to the other.

They solve slightly different problems.

And then there is the baseplate itself.

This is where pouch selection becomes much more individual than a simple one-piece-versus-two-piece chart can capture.

Different products use different adhesive formulations and baseplate designs.

Some are firmer.

Some are softer.

Some are designed to flex particularly closely with the abdomen.

Some extend differently around the body.

The skin beneath them matters too.

Because the ideal pouch isn't merely one that successfully collects urine.

It needs to create a reliable seal without making the skin underneath miserable.

Recent research involving people using urostomy products found that skin protection, comfort, leak prevention, ease of use, compatibility with night drainage and durability were among the features people considered particularly important. Urostomy Association

Which sounds obvious.

Until you remember that somebody may be wearing this device 24 hours a day, seven days a week.

Tiny differences stop being tiny when something lives on your abdomen.

What about barrier rings and seals?

These aren't technically another type of pouch, but you'll encounter them very quickly when talking about pouching systems.

A barrier ring or seal can sit around the stoma beneath the baseplate.

It can help fill small gaps, creases or uneven areas and create a closer seal between the appliance and the body.

There are also pastes, strips and other accessories designed to help with particular fitting problems.

But more products don't automatically mean a better pouching system.

Sometimes the solution to a leak is an accessory.

Sometimes it is a different baseplate.

Sometimes the opening is the wrong size.

Sometimes the stoma or abdomen has changed.

And sometimes the entire pouch simply isn't the right product for that person.

Which is why persistent leakage is something to discuss with a stoma nurse rather than endlessly building increasingly elaborate architecture around the stoma yourself. The

Urostomy Association advises seeking specialist help if leaks continue. Urostomy Association

Night drainage changes things again.

Urostomies have another practical consideration:

Urine keeps coming overnight.

Rather than repeatedly getting up to empty a pouch, many people connect their urostomy pouch to a larger night drainage bag.

The connection allows urine to drain away while they sleep.

That means compatibility with night drainage systems can be an important part of choosing an appliance — and it was specifically identified as important by urostomy users in recent research. Urostomy Association

It's another example of why the “best” pouch isn't necessarily the one that looks nicest sitting unused in a sample box.

It is the one that works at 3am.

And under clothes.

And when you're travelling.

And when you're sitting down.

And when you're moving.

Real life is the ultimate pouch test.

Transparent or opaque?

Another apparently small choice that can matter enormously.

Some pouch systems allow the stoma and urine to be seen more easily through the front of the pouch.

Others provide more opaque coverage.

Immediately after surgery, visibility can be extremely useful while somebody is learning how their stoma behaves, and healthcare professionals need to observe it.

Later, some people prefer greater discretion.

Others like being able to check their stoma or urine easily.

There isn't a morally superior answer to this either.

It's your abdomen. You're allowed preferences.

The tap matters more than you might imagine.

At the bottom of a urostomy pouch is the outlet used to empty urine.

Different products have different tap or bung designs.

This sounds like the least exciting engineering discussion imaginable until you remember that you may operate this little mechanism several times every single day.

Then things like grip, dexterity, reliability, ease of cleaning, how confidently it closes and how easily it connects to night drainage become rather important.

Recent UK research into urostomy devices specifically highlighted simple and accessible taps as an important feature, particularly for people with reduced dexterity or sight loss. Urostomy Association

A tiny piece of plastic can have a surprisingly large effect on independence.

The pouch you leave the hospital with isn't necessarily your pouch forever.

I think this is one of the most important things for somebody new to a urostomy to know.

You have options.

The pouch used immediately after surgery may work brilliantly for you for years.

Or it might not.

Your abdomen changes as you recover.

Your stoma settles.

Your routines change.

Your weight may change.

You become more active.

You discover what you like and what drives you absolutely mad.

And products themselves continue to evolve.

The Urostomy Association says people are entitled to impartial advice about the urostomy pouches most suited to their needs and recommends discussing options with a stoma nurse. Urostomy Association

That is particularly important because 2026 research highlighted a worrying finding: some people thought the pouch they were given after surgery was simply the only type available to them. Urostomy Association

It isn't. I tried about five different brands of urostomy pouch before I found the one which worked for my skin. Even now, I can still experience a reaction to the adhesive of my favourite brand! When that happens, I simply swap to an old sample kit that I was offered by a different company for around 48 hours so that my skin can settle down. Sometimes a slight change for a small amount of time is helpful.

Finding the right pouch is not a vanity project.

A leak isn't simply inconvenient.

Sore skin isn't simply uncomfortable.

A difficult tap isn't simply annoying.

A pouch somebody doesn't trust can affect whether they sleep properly.

Whether they exercise.

Whether they wear particular clothes.

Whether they travel.

Whether they go swimming.

Whether they sit through a meeting without wondering what is happening underneath their shirt.

Whether they leave the house without packing enough emergency equipment to survive a minor expedition.

Research commissioned by the Department of Health and Social Care and conducted by National Voices found that people using urostomy products described problems with leakage and appliance design affecting confidence and mental wellbeing. Urostomy Association

So finding the right appliance isn't cosmetic fussiness.

It can be part of getting your independence back.

So which urostomy pouch is best?

I'm afraid this article ends with the most irritating answer in healthcare: it depends.

One-piece or two-piece.

Flat or convex.

Cut-to-fit or pre-cut.

A particular adhesive.

A particular shape.

A particular tap.

Perhaps a barrier ring.

Perhaps not.

The right combination depends on the stoma, the abdomen, the skin, dexterity, lifestyle and — importantly — the person wearing it.

And sometimes finding that combination takes experimentation.

Samples.

Conversations.

A few failures.

Possibly some language directed towards an adhesive medical appliance that cannot be repeated on a respectable urinary-health website.

And then, hopefully, the pouch becomes boring.

Because I think that's ultimately the dream.

Not spending every waking hour thinking about your urostomy.

Not constantly checking for leaks.

Not wondering whether the seal is holding.

Just trusting the little piece of medical engineering attached to your abdomen enough to get on with everything else. In fact, there are days where I even forget I'm wearing mine!

Because a good urostomy pouch doesn't need to be the centre of your life.

It should help you live it.

Oui. Together, we can. 💛

A note from Oui

Oui provides health information and lived-experience discussion, not individual medical advice.

Persistent leaks, sore or damaged skin, changes in the shape or position of your stoma, or difficulties getting a pouch to fit properly are worth discussing with a stoma care nurse. Different appliances and accessories suit different bodies, and specialist assessment can help identify an appropriate system. Urostomy Association

References & Further Reading

Urostomy Association (2026). What is a urostomy? Covers ileal conduits, urostomy pouches, one- and two-piece systems, pre-cut and cut-to-fit products. Urostomy Association — What is a urostomy?

Urostomy Association. Three simple steps to preventing leakage. Information about pouch fit, flat and convex skin barriers and managing leakage. Urostomy Association — Preventing leakage

Urostomy Association (2026). Understanding issues that may arise with a urostomy. Includes information on appliance choice, leakage and seeking advice from a specialist stoma nurse. Urostomy Association — Understanding urostomy issues

Urostomy Association (2026). Research highlights what urostomates need from NHS medical devices. Reports findings from Department of Health and Social Care-commissioned research into what matters to people using urostomy appliances. Urostomy Association — What urostomates need from medical devices

Urostomy Association (2026). You can handle this. Practical guidance on pouch fit, barrier products, convexity and leakage. Urostomy Association — You can handle this