Last updated: 20 October 2026
Choosing between a single-fin and double-fin shower door bottom seal isn't just about the number of blades. What matters most is the gap between the bottom of the glass and the shower tray or bath rim.
In SIMBA's current range, double-fin seals are mainly suited to smaller gaps of around 4–8mm. For larger gaps, a single-fin seal with the right coverage is often a better starting point.
Before choosing either type, check your glass thickness and bottom gap.
Single Fin vs Double Fin: What's the Difference?
A single-fin seal has one flexible blade that sits close to the tray or lightly touches it, helping direct water back into the shower. Single-fin profiles are available in different lengths, making them suitable for a wider range of bottom gaps.
A double-fin seal has two flexible blades. The extra edge can help control water in smaller gaps, provided both fins have enough room to sit properly without making the door difficult to move.
Two fins don't necessarily mean better sealing. If the gap is too large, the blades may not reach the tray. If it's too tight, they can create unnecessary friction.
Which Seal Suits Your Bottom Gap?
For the SIMBA profiles discussed here, these are useful starting points:
| Bottom gap | Seal worth considering |
|---|---|
| Around 4–8mm | Double-fin seal |
| Around 5–11mm | 12mm single fin |
| Around 11–15mm | 16mm single fin |
| Larger gaps | 20mm or 23mm single fin, depending on the required coverage |
These ranges are a guide, not a guarantee of fit. Check the individual product's glass thickness and gap coverage before ordering.
A longer fin isn't always better, either. If it's much longer than the gap, it may fold against the tray or make the door harder to move. A stiffer fin can sometimes leave a small opening near the hinge instead of sealing it. That's why choosing the longest fin available isn't necessarily the safest option.
What Else Should You Check?
If your old seal worked well before it became worn or damaged, a similar profile may be a good starting point. Bear in mind that an old fin can become bent or flattened, so don't rely on its current shape alone.
We usually ask customers for three things when helping them choose:
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Glass thickness
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Bottom gap
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A photo of the old seal's end profile
Once you have those details, you can compare options in our shower door bottom seals range. Start with Glass Thickness, then check Gap Coverage.
If you'd like a closer look at the different seal shapes and measuring methods, our guide to shower door bottom seals covers them in more detail.
Not Sure Which One to Choose?
Send us a few photos and measurements, and someone from the SIMBA team will help you check the fit.
If we've recommended the wrong seal, we'll review the fitting details and put it right. Where our recommendation was based on accurate information you provided, we'll arrange a suitable replacement at no extra cost, or give you a full refund if we can't find one.