Last updated: 17 June 2026
It is easy to assume a new shower door seal is suitable once it clips onto the glass and the door closes. The problem often appears later, when the door starts to drag, squeak or pull the seal loose from one end.
We saw this recently with a customer whose shower door had an 11mm gap at the bottom. She had fitted an 18mm bottom seal bought from Amazon. The deeper fin sounded like the safer option, but it pressed heavily against the shower tray and dragged every time the door opened.
The seal was not simply falling off. The movement of the door was gradually pulling it away from the glass.
A vertical seal can fail in a different way. It may look secure when first fitted, then slowly slip down after the door has been opened and closed a few times. Water has not washed it off. The channel is usually too loose to hold the glass properly.
Before replacing the seal again, look at how it is moving. A bottom seal is often dragged off by the door. A vertical seal is more likely to slip because the channel is not gripping the glass firmly enough.
Is the Seal Being Dragged Off or Sliding Down?
Start by watching what happens when the door opens.
At the bottom of the door, the signs are usually easy to feel. The door may be tighter than before, the seal may rub against the tray, or the fin may bend and curl as it moves. The strip may then begin to work loose from one end.
In that situation, the seal is probably too deep for the space under the glass.
A side seal behaves differently. The bottom of the door may move normally, with no scraping or stiffness. Instead, the vertical strip gradually slips down the glass. You push it back into place, it stays there for a while, and then moves again after a few uses.
For a bottom seal, check the gap under the glass. For a side seal, check the fit of the channel. Copying the old seal without checking either measurement can leave you with the same problem again.
Bottom Seal: Deeper Does Not Mean Better
A bottom shower door seal should make light contact with the tray or threshold. It needs to help direct water back into the enclosure without making the door difficult to move.
If the actual gap is 11mm and an 18mm seal is fitted, the extra depth has nowhere useful to go. The fin is forced to bend against the tray and drag whenever the door moves.
At first, this may only show up as a squeak or a slightly stiff door. Over time, the fin can curl, the strip can shift, or the whole seal can begin to pull away from the glass.
That is not stronger sealing. It is resistance caused by the wrong size.
When a bottom seal keeps coming off, pushing it on more firmly is unlikely to solve the problem. Check whether the fin is too deep for the actual gap.
The fin still needs to reach the tray, but a longer bottom fin is not always a better fit if it has to bend heavily every time the door moves.
Vertical Seal: Fitting Over the Glass Is Not the Same as Holding It
A vertical shower door seal relies on the U-shaped channel gripping both sides of the glass. A neat-looking fit is only the starting point. If the channel is slightly too loose, the seal can still begin to move after repeated use.
A common problem is a channel that is wider than the glass requires. For example, a seal intended for thicker glass may slide easily onto a 6mm panel but fail to hold it securely.
After a few door movements, or after being touched during cleaning, the strip can start to move down the glass.
This is where some so-called universal seals disappoint. Being easy to fit does not necessarily make them a good match.
If a vertical seal keeps slipping, check the glass thickness, channel size and profile. Fixed panels, hinged doors, closing edges and glass-to-glass gaps can all require different shapes, even when the seals look similar from the front.
Do Not Copy the Old Seal Blindly
The old seal is not always a reliable guide. It may have hardened, stretched, flattened or distorted over time. In some cases, it was the wrong size from the beginning.
Before ordering a replacement, confirm at least two measurements.
Glass thickness matters for the U-channel, while the bottom gap determines the seal depth. Both are basic parts of measuring and fitting a replacement seal, but they are often missed when the old profile is copied by appearance alone.
For a bottom seal, measure the gap with the door closed. Check the left side, centre and right side rather than relying on a single point. Older shower doors can drop slightly, and the tray may not be perfectly level.
It is also better to measure the glass rather than relying only on the old seal. A worn channel may no longer reflect the size it was originally designed to fit.
Glue Is Usually Not the Right Fix
When a shower seal keeps falling off, silicone or glue can seem like a quick answer. If the size is wrong, it only hides the problem for a while.
A bottom seal that is too deep will still drag against the tray. A vertical seal with a loose channel still will not grip the glass properly.
A push-on seal should stay in place because it fits the glass correctly, not because it has been glued into position. If adhesive is the only thing holding it on, the seal is usually not the right fit.
Glue can also make the next replacement more difficult and leave residue on the glass. It is better to correct the size or profile than to secure an unsuitable seal permanently.
Choosing the Replacement
If the bottom seal is being dragged
Check the bottom seal first if the strip comes away from the base of the glass and the door feels stiff, rubs against the tray, squeaks or bends the fin heavily during movement.
The main question is not whether the seal can be pushed on more firmly. It is whether the fin depth matches the real gap under the glass.
Once the glass thickness and bottom gap are known, choose the replacement using both measurements rather than fin depth alone.
If the side seal keeps slipping
Check the vertical seal if it slides down the side of the glass or is pushed out of position when the door closes.
This usually comes down to glass thickness, channel size and profile. A seal can slide onto the glass and still be too loose for regular use.
The replacement needs to match not only the glass thickness, but also the way the door closes and the position the seal is expected to cover.
What to Check Before Replacing the Seal Again
The way the seal fails usually points to the measurement that matters.
If it is being dragged away at the bottom, check the real gap under the glass. If it is slipping down the side, check the glass thickness and channel fit.
An 11mm gap fitted with an 18mm bottom seal may appear to provide more coverage, but it can make the door drag and gradually pull the strip away. A vertical seal that slips down usually needs a closer match to the glass and a firmer channel.
The suitable replacement shower door seals therefore depend on how the old seal is failing, not only on how its profile looks.
If you are still unsure, send us a clear photo of the glass edge and the gap under the door before ordering.
About Simba
Simba was founded in 1998 and focuses on the manufacture, testing and replacement support of shower door glass seals. This article is based on customer feedback, product measurements and selected grip-force testing.