Why Bulb Shower Door Seals Never Be Installed at the Bottom

1. Introduction

When it’s time to replace a bottom shower door seal, most people do one thing:

They copy whatever was there before.

“Looks the same? That’ll do.”

But here’s the problem — just because it looks the same doesn’t mean it works the same.

Especially when it comes to bulb shower door seals.

They look like they fit. But install one at the bottom of your shower door, and you’re asking for trouble.

These seals aren't made to stop water. They’re made to seal gaps — not to block floods.

Put one at the bottom and here’s what can happen:

• Water leaks out.
• Water stays inside the seal.
• Mold, bad smells, even jammed doors or shifted glass panels.

So in this post, let’s set the record straight.

We’ll cover:

• What bulb shower door seals are really for
• Where they should be used
• And why installing them at the bottom is a mistake you don’t want to make

Let’s dive in.

 

2. What Is a “Bulb-Style” Shower Door Seal?

Don’t let the word “bulb” throw you off.

We’re not talking about soap bubbles here.

A bulb seal is a shower door seal with a rounded, air-filled section at the top — kind of like a tiny balloon built into the strip.

You’ll often find this type of seal along the vertical edge of your shower door, or the side that sits close to the wall.

Take this one for example — the SIMBA-0014a.

It’s made for 6mm glass and 8mm glass and is a classic vertical shower door seal.

So why the “bulb” design?

Here’s the deal:

• Bulb seals are made of soft PVC.
• Inside the bulb is air — which gives it a cushion-like structure.
• When the door closes, the bulb compresses slightly, then springs back.
• That creates a gentle but snug seal between the glass and the frame.

 

Here’s the key point:

Bulb seals are designed for side sealing — not for blocking water from below.

Install one at the bottom of your shower door and things go south quickly.

• Water collects inside.
• Mold starts growing.
• And worst of all? It’s almost impossible to clean.

You might be thinking:

“But my old bottom seal looks like that — it has a round bulb in the middle!”

Yep. We’ve seen that too — especially on some popular online models.

They look like bottom seals.

But that “bulb” in the center is the issue.

It traps water.

It hides grime.

And over time, it turns into a dirty, smelly mess.

Next, we’ll show you exactly why bulb seals don’t belong at the bottom — and what to use instead.

 

 

3. Why Bulb Seals Should Never Go at the Bottom

Let’s get straight to the point:

If your seal has a bulb, it doesn’t belong on a flat surface.

No exaggeration — it’s just not built for the bottom of your shower door.

Here’s why:

 

1. Tiny gaps = Big leaks

Bulb seals are hollow inside.

When you install one at the bottom, gravity and the weight of the door press it down.

At first, it might look like it fits.

But here's the issue: the seal needs to be perfectly aligned to block water.

Even a 1mm gap can lead to leaks.

And in the real world? Gaps happen.

Water seeps through. Every. Single. Time.

2. It traps water — and grows mold

Bulb seals aren’t made to drain water.

There are no channels, no slopes, no exit paths.

So what happens when water gets in?

It stays.

And when water sits, mold grows.

Bad smell follows.

Eventually, the seal starts to break down.

The worst part? You can’t clean it.

The only fix is to rip it off and replace it.

3. It can’t handle pressure

Bottom seals take a beating.

• Door opens and shuts multiple times a day.
• The seal rubs against the floor or threshold.
• It has to bounce back, over and over again.

Bulb seals aren’t built for that kind of stress.

They crack. They flatten. They deform.

Once that happens, it’s game over — the seal won’t do its job anymore.

 

4. It’ll cost you more in the long run

Using the wrong seal = faster wear and tear.

And that means:

• More returns
• More replacements
• More wasted time and money

So here’s the golden rule:

That soft “bulb” is meant for sealing side gaps — not blocking water or holding weight.

In the next section, we’ll show you where bulb seals actually belong — and which seals are best for the bottom of your shower door.

 

5. Bulb Seals Block Smooth Opening

Installing a bubble-shaped seal at the bottom can make the shower door difficult to open and close.

One of our clients used this type by mistake and found the door couldn’t open smoothly at all.

 

 

4. The Right Way to Use a Bulb Seal: Where It Actually Belongs

 

A bulb seal isn’t a magic fix.

Put it in the wrong spot, and it causes more problems than it solves.

So, where should it go?

The side. Always the vertical side.

That means:

• Between the shower door and the wall
• Between two glass panels that close against each other

Why the side? Let’s break it down.

 

1. It handles side pressure perfectly

When you close your shower door, that soft bubble compresses gently.

It fills the gap without making the door hard to close.

Nice, tight seal.

No rattling. No banging.

Just a soft cushion with a watertight fit.

 

 

2. Vertical edges are gentler on seals

The bottom of your shower? It’s brutal.

• Constant water flow
• Dirt and soap scum
• Friction from opening and closing
• Even the occasional footstep

A bulb seal isn’t built for that.

But on the vertical edge?

No standing water. No major pressure.

Just light contact — so the seal lasts longer and keeps its bounce.

 

 

3. It prevents glass-on-glass damage

If you have a frameless door, you don’t want glass slamming into glass.

Our SIMBA model SIM-0014A is designed exactly for this:

• Fits 6–8mm thick glass
• Perfect for 180° glass-to-glass doors
• No gaps, no harsh edges — just a clean, smooth seal

 

So... What should go at the bottom?

Worried about leaking at shower door bottom?

Don’t improvise with a bulb seal.

Use a proper shower door bottom gasket instead.

Here are a few good options:

• Single-fin seal – One flexible fin to deflect water inward
• T-shaped seal – Angled to guide water back into the shower
• Double-fin seal with drip rail – Two fins for extra coverage and better drainage

All these plastic strip at the bottom of your shower door are made for horizontal use.
They direct water flow, don’t trap moisture, and are built to handle wear.

 

In short:

Bulb seals are perfect for side sealing — not water blocking.

For the bottom, go with seals designed for water drainage.

Up next: a quick checklist to help you choose the right bottom seal — and avoid future headaches.

 

5. How to Choose the Right Bottom Seal for Your Shower Door

Choosing a bottom seal isn’t about guessing or “close enough.”
It’s about precision.

Here’s a quick measure guide to get started:

 

Step 1: Measure Your Glass Thickness

Is it 6mm? 8mm? Measure it with a caliper or ruler to be sure.

 

Step 2: Measure the Gap at the Bottom

How much space is there between the door and the floor or threshold?
You’ll need this to find a seal that fits snugly — not too tight, not too loose.

 

Step 3: Measure the Required Length

Most shower doors are around 900mm wide — but don’t assume.
Measure it directly so you can cut the seal to size or buy the perfect length.

Example:

Let’s say your measurements are:

• Glass thickness: 6mm
• Bottom gap: 12mm
• Seal length: 900mm

Head to our bottom seal page and use the filter on the left-hand side:

Just plug in those numbers — the system will show you all matching options.

In this example, you’ll see 3 matching seal strips that fit your door perfectly.

One Last Warning:

You might spot a model like SIMBA 0009 — it has a triangle-shaped, hollow chamber.

Looks interesting? Maybe.

But we don’t recommend using it at the bottom.

Why?

Because just like a bulb seal, that “bubble chamber” design traps water,

making it hard to clean — and over time, it can lead to mold, odor, and stains.

 

 

Our Recommendation?

Stick to the other two options with smarter, cleaner designs.

Both are engineered for water drainage, durability, and easy maintenance.

Choose the right seal, and you’ll stop leaks before they start — for good.

 

 

Easy to Cut, Simple to Install

All SIMBA bottom seal strips come in a standard 950mm length.

You just trim them to fit your specific door size.

We offer 3 easy cutting methods — all suitable for regular home DIYers.

Each seal also includes a free transparent water-retaining threshold strip.

It enhances water blocking and should be trimmed to match your shower door width.

If you have any questions about selecting, trimming, or installing your seal strip, don’t hesitate to reach out:

Email us at info@showerdoorseal.uk

Or message us directly via WhatsApp — we’ll get back to you as soon as possible.

 

6. Summary & Pro Tips

Bulb seals aren’t meant to do it all.

They’re great for cushioning and vertical sealing, but not built to handle water flow at the bottom of your shower door.

Using a bulb seal at the bottom might seem fine at first glance — but it often leads to:

• Water pooling and mold buildup
• Leaks due to poor compression
• Deformation and short lifespan

Here’s our honest advice:

If you're replacing a bottom seal, stick with seals that are designed for horizontal surfaces — not bulb seals.

Still not sure what to choose? Just send us your glass thickness and gap size — we’ll recommend the right fit for free.

Every SIMBA seal is purpose-built to solve specific problems — no guesswork, no mess.

Choose the right seal once, and avoid all the hassle later.

🔗 Featured Articles

1. How To Measure Shower Screen Seal? (Buying Guide)
2. How To Cut Shower Door Seal Easy?
3. How To Replace Shower Screen Bottom Seals
4. Shower Screen Seal: Which Way Round Should It Go?
5. Why Is Your Shower Door Leaking at the Bottom?
6. 5 Golden Rules to Choose the Right Shower Door Seal