Sash Windows: Compression Seals vs Brush Seals - Myths Debunked!
Why a Brush Seal is Far Superior to a Compression Seal for Draught-Proofing Double Hung Sash Windows
One of the most common questions we get from homeowners looking to improve the energy efficiency of their timber sash windows is:
“Should I use a brush seal or a compression seal?”
It’s a great question — and the answer is clear. When it comes to draught-proofing double hung sash windows, brush seals (such as those inserted in our Stop Beads and Parting Beads ) are far superior to compression seals (like Schlegel Aquamac and similar). Let’s break down why.
What’s the Difference Between Compression and Brush Seals?
To choose the right seal, you need to understand what each type is designed to do:
-
Compression seals are made to be squeezed between two closing surfaces — such as in a casement window or a door. They only work properly when there’s a tight, compressed fit.
-
Brush seals are designed specifically for sliding applications, like double hung sash windows. Instead of relying on pressure, the brush bristles create a flexible barrier that moves with the sash and seals the gap without restricting movement.
Why Compression Seals Don’t Work in Sash Windows
Sash windows slide vertically — they don’t compress shut. That’s the key reason why compression seals just aren’t suitable.
Here’s what typically goes wrong:
1. Too Much Friction
Compression seals create resistance. This makes sash windows harder to open and close, especially if they’re older, heavier, or slightly out of alignment.
2. Faster Wear and Tear
Because they aren’t designed to move, compression seals break down quickly in sliding applications. You’ll find they flatten, tear, or detach after relatively little use.
3. Poor Draught Sealing
Compression seals need to be compressed to do their job. If they’re installed in a sash window, they don't always seal fully — leaving you with gaps, draughts, and noise.
Why Brush Seals Are the Perfect Fit
Brush seals are made for movement — that’s why they’re ideal for sash windows. The fine bristles flex with the timber and create a consistent seal, even as the window moves.
Here’s what makes them stand out:
-
Low-friction sliding — Your windows open and close effortlessly.
-
Durable performance — High-quality brush seals withstand years of use without losing their shape.
-
Reliable sealing — They block draughts, dust, insects, and noise — all without stiffening or jamming the sash.
Not All Brush Seals Are Created Equal
Here’s where Lock and Latch’s draught-proofing products really shine.
Unlike many brush seals on the market, our products feature a plastic fin embedded within the brush hairs. It’s this central fin that forms a complete and continuous seal — delivering superior draught-proofing without compromising smooth operation.
So if you’ve ever heard that “brush seals don’t form a proper seal,” that’s a myth — at least when it comes to ours.
Built Into the Best: Our Premium Window Kits
We don’t just sell brush seals — we build them into every one of our draught-proofing systems.
All of our:
Come pre-fitted with our fin-equipped brush seals. This attention to detail is why we proudly call our range:
“The Rolls-Royce of sash window draught-proofing products.”
You’re not just getting a seal — you’re getting a complete, long-lasting, high-performance solution.
When Should You Use a Compression Seal?
Compression seals aren’t bad — they’re just not right for sash windows.
They’re ideal for:
-
Casement windows
-
Front and back doors
-
Any situation where a firm, compressed seal is created when the window or door is shut
The Bottom Line
If you're looking to draught-proof your timber double hung sash windows properly, brush seals are the clear winner.
And with Lock and Latch’s advanced fin-brush technology, you get a complete seal, smooth operation, and long-lasting performance — all in one.
Need Help?
Not sure what you need for your sash windows?
Get in touch — we’ll be happy to help you choose the right draught-proofing solution for your home.
