Last updated: 29 April 2026
Expert Tip: This guide has been reviewed by James Liu, SIMBA’s in-house sealing specialist, who works with shower seal design, fitting guidance, and customer troubleshooting.
In our 7-day hard water test in a London bathroom, the incorrectly installed shower door seal leaked in 9 out of 10 water-flow checks around the shower doorway.
If you’ve ever muttered “shower screen seal – which way round?” while wrestling with a stiff plastic strip, you aren't alone.
Getting it the wrong way round is one of the most common reasons for shower door leaks.
But here’s the thing: many product pages focus on size and glass thickness, but don’t clearly show seal direction.
Already know what you need?
If you've diagnosed the direction and just need a professional-grade replacement, browse our full collection of UK Standard Shower Screen Seals to find the perfect fit for 4mm to 12mm glass.
In this guide, SIMBA will walk you through how to tell which side faces in, which faces out, and go through common types with simple tips to get it right.
Is your current shower enclosure seal really suitable? Explore our expert sealing solutions for all types of shower enclosures.
Quick Self-Diagnostic: Did I get it wrong?
Case A: Puddles on the floor but the seal looks new? → Diagnosis: Your drip rail is likely facing outwards, acting as a bridge for water to escape.
Case B: Door is hard to push closed or "springs" back? → Diagnosis: Your vertical fin is too long or facing the wrong way against the frame.
1. Bottom Drip Rail Seals: Which Way Round?
Seen this type before? It’s the most common bottom door seal for shower door designs.
That slanted bit on the side (marked 1️⃣) is called the Drip Rail.
Drip Rail Explanation:
The drip rail acts like a slide, directing water back into the shower tray before it even reaches the bottom fin. This reduces the pressure on the soft fin (marked 2️⃣) and prevents puddles on your floor.
A word of advice:
Not every seal strip features a well-designed drip rail. Quality matters for a watertight finish.
Which way round does a drip rail shower screen seal go?
The no-nonsense rule: The drip rail (the slanted edge) always faces into the shower.
Think of the drip rail as a gutter. If the angled drip rail faces out, it acts as a water bridge, guiding water directly onto your bathroom floor.
Shop the Range: Replacement Bottom Seals with Drip Rails – Available for 4mm to 12mm glass.
Why "Standard" Bottom Seals Aren't Always Enough
At SIMBA, many of our shower door bottom gaskets include a free threshold strip—the plastic bar that sits on the floor.
Need more help with sizing? Explore our The Ultimate Guide to Shower Door Bottom Seals for a step-by-step walkthrough.
A Word of Caution on Bulb Seals
You might see these bulb seals sold as "universal," but these seals are rarely suited for the bottom of a door.
The Problem: They trap limescale and black mould inside the bulb, making them impossible to clean. The Result: They perish much faster than a proper single-fin drip rail seal.
Especially in hard water areas like London, bulb seals become a magnet for stubborn limescale.
Instead, we recommend our Heavy-Duty Single Fin Sweep, which is designed specifically to prevent mould buildup.
2. Seal at Bottom of Shower Door with Dual Fins
(Long fin + short fin combo)
They come with two soft fins sticking out – one long, one short. The rule remains the same:
- Long fin goes INSIDE the shower
- Short fin faces OUT
Why? The longer fin stops splashes and directs water back inside. The short one acts as a backup. Together, they work like a mini curtain.
Bonus tip: If the gap is narrow, trim the long fin to match the short one.
3. For 180-Degree Glass (Side & Vertical Seals)
The U-shaped part is rigid, and there’s one soft fin coming out the side. This is a classic 180-degree H-shape seal profile.
Direction: The soft fin should face INWARDS, into your shower.
This advice assumes your shower door opens outwards, which is common for safety and access reasons. Always check your own enclosure design before fitting.
The Rule: Door opens out = Fin goes inwards.
View our full range of 180° H-Shape Vertical Seals available for 6mm, 8mm, and 10mm glass.
4. Y-Shape Shower Door Seal
Designed for 135-degree angled glass panels.
The Rule: The soft fin always faces INSIDE the shower.
Note: This same rule applies if you are using this profile as a frameless Y shape vertical shower door seal on a 90-degree sliding door.
Need a replacement for a diamond-shaped enclosure? Our Y-shape seals are the specialist choice.
Not sure if you need a Y-shape or a standard H-profile? Check out our The Vertical Seal Masterclass: F-Shape, H-Shape to identify your exact enclosure type.
5. Which Way Should a Magnetic Shower Seal Face?
There are two main types of magnetic shower door seals:
1. Flat-top magnetic seals
Universal fit for 180° setups. Symmetrical design, so there is no "wrong" side.
2. Angled-top magnetic seals
Designed for specific 90° or 135° corner enclosures. The General Rule: The longer edge faces outward; the shorter edge faces inward. If your door opens inward, flip that around.
Expert Tip: To take the guesswork out of your DIY project, we’ve added clear directional labels to all SIMBA seals. If you are dealing with a more complex setup, such as pivoting or folding doors, you might find my Masterclass on Magnetic Shower Seals helpful — it’s a deep dive into alignment and polarity I’ve put together based on years of manufacturing experience. —— James, Founder of SIMBA
6. Frequently Asked Questions
Which side of a drip rail seal faces in?
The slanted drip rail (the hard plastic part) acts as a water slide and must always face inside the shower cubicle. If it faces out, it channels water onto your floor.
Does the long fin or short fin go inwards?
The long fin always faces in. It acts as the primary barrier against splashes. The short fin is just a secondary wiper.
Can I use warm water or a hairdryer to soften the seal?
We strongly advise against this. While heat makes the PVC pliable for installation, it permanently alters the polymer structure, causing the seal to lose its "memory" and grip. Within weeks, it will slide down.
💡 Better Solution: Best way install your shower seals
Can I use soapy water to help with installation?
No. Soap leaves a residue that feeds black mould and can cause the PVC to turn yellow (oxidise) faster. It also reduces the friction grip on the glass.
Why won’t my door close after fitting the new seal?
This is usually a seal's fin length issue. If the fin is too long, it hits the frame, floor or the opposite side seal, creating resistance.
What should I do if the seal keeps sliding down?
This indicates a glass thickness mismatch. If your glass is 6mm but the seal is for 8mm, gravity will win.
For a permanent fix, check our [Guide to Measuring Glass Thickness].
7. Final Thoughts
If your seal looks different or isn’t listed, look at the soft fins. Still not sure? Don’t risk buying the wrong size.
Not sure if your seal is 'Standard' or 'Specialist'?
Click here to upload a photo - our experts will mark the correct orientation and send guidance back as quickly as possible, usually within one working day.
The SIMBA Promise: We don’t just send you a seal. Every order includes Clear Installation Guides to make your DIY project a success.