By friction alone.

Sprung between two opposing walls.

The outward force holds it there.

Which is plenty for a wet curtain.

And nothing else at all.

A sideways or downward load.

Somebody grabbing it or leaning on it.

Or catching it while falling.

It comes down when that happens.

And comes down with the person.

Where anyone has limited balance.

Which is most bathrooms with a shower seat.

Or a grab bar already fitted.

It looks like something to hold.

And is not.

Only as strong as its wall fixings.

Which is rarely a grab bar's rating.

But it does not fail on being touched.

If somebody may need support.

Fit a grab bar and remove the question.

Real shoulder room inside the curtain.

By bowing outward from the wall.

Without changing the tray or bath.

So the curtain stops touching the user.

Which is the usual complaint.

For exactly that reason.

A standard bath feels much larger.

For the cost of a different rod.

With no building work.

It is a cheap upgrade.

So the curtain hangs inside the rim.

Not merely so the rod spans the gap.

Height sets where the hem falls.

And horizontal position sets which side.

Both decide whether the curtain works.