Secondary Glazing Glass Types: Which Should You Choose?
You’ve decided on secondary glazing. Now comes the next question: which glass type should you go for?
Most suppliers give you a list of options with no explanation of what actually changes between them. The answer matters, because the glass you choose directly determines how much noise you block out or how much warmer your rooms become. This guide uses real performance data to help you make that decision with confidence.
Standard Toughened Glass: The Default Starting Point
Clearview’s standard specification is 4mm toughened clear glass. It gives you approximately 45dB sound reduction and meets building regulations’ safety requirements for glazed panels.
Toughened glass is the baseline because it’s safe. If a panel breaks, it shatters into small, relatively harmless fragments rather than sharp shards. On panels above 1.6m², Clearview automatically upgrades to 6mm toughened glass as standard, which brings noise reduction up to around 49dB.
Standard 4mm toughened is the right choice if your main concern isn’t noise or thermal performance, if you’re glazing a listed property where visual subtlety matters most, or if you want the most cost-effective option.
6mm Toughened Glass: A Simple Noise Upgrade
A step up from the standard 4mm, 6mm toughened glass is Clearview’s automatic upgrade for larger panels. It’s worth specifying on smaller panels too when noise reduction is the primary concern, without stretching to acoustic laminate.
At 49dB+, 6mm toughened sits meaningfully ahead of 4mm standard. To put that in context: a 3dB increase halves the energy of the noise reaching you. The jump from 45dB to 49dB is a noticeable improvement in practice.
Acoustic Laminate Glass: For Serious Noise Reduction
If you live on a busy road, near a railway line, or in an area with persistent urban noise, acoustic laminate glass is worth the upgrade.
Clearview uses Stadip Silence PVB acoustic laminate, available in two specifications:
6.4mm Stadip Silence delivers approximately 51 to 53dB sound reduction. The PVB (polyvinyl butyral) interlayer damps vibration as sound passes through the glass, targeting the frequencies that standard toughened glass lets through. It carries Class B safety rating.
6.8mm Stadip Silence achieves the same 51 to 53dB range but performs better at high frequencies, including traffic noise and voices, and carries a Class A safety rating. If road or railway noise is the main problem, 6.8mm is the stronger choice.
Customer Kevin Millard put it plainly: “The difference in noise is amazing. I went for the 6.4mm laminated glass and positioned the units to give maximum gap.”
For anyone ordering acoustic secondary glazing with serious noise reduction as the goal, we recommend 6mm toughened as a minimum and 6.4mm or 6.8mm laminate for the best results.
Low-E Glass: For Thermal Performance
Pilkington K Glass is our Low-E option. The K glass designation refers to the hard coating applied to one side of the glass surface. That coating reduces infra-red heat radiation through the glass, which is a significant proportion of total heat loss through a window.
The coating must face into the room. We fit it that way as standard, so you don’t need to worry about it. In practice, Low-E glass:
- Achieves a certified U-value of 1.868 W/m²K, the same thermal performance range as double glazing
- Provides a 65% insulation improvement versus standard single glazing
- Can reduce yearly heating bills by up to 15%
- Is available in 4mm and 6mm specifications
Glasgow University research, carried out for English Heritage and Historic Scotland, confirmed that secondary glazing with Low-E glass outperforms double-glazed replacement windows in traditional buildings, a relevant finding for anyone with period property sash windows.
Matthew James, who fitted Clearview units to a Grade II listed property built in 1850, described the result: “Best investment in my property so far. Since I fitted the units, condensation has been eliminated, there are no more draughts, and external noise has been greatly minimised. They’re so good I’ve yet to put the heating on this year.”
Low-E glass is the right choice for cold rooms, draughty sash windows, listed buildings where thermal insulation secondary glazing is the priority, or landlords working toward EPC C compliance.
Ultra-Panel: Maximum Acoustic Performance
The Ultra-Panel uses 10.8mm acoustic glass and delivers the highest sound reduction in the Clearview range. It requires the Ultra Profile frame, which is worth noting when you’re ordering.
If you’re in an extreme noise environment and want the best result possible, this is the option. It’s a significant upgrade in both performance and cost relative to standard acoustic laminate.
Vision HD Sealed Unit: Commercial Grade
The Vision HD Hinged Casement accepts a 28mm sealed double-glazed unit. This is the only product in the Clearview range that accommodates a full DGU cavity, making it the right choice for commercial applications that need double-glazing-equivalent performance from a secondary glazing system. Pricing is on application.
How to Choose: Matching Glass to Your Situation
| Your main concern | Glass to choose |
|---|---|
| General use, listed building, budget | 4mm toughened (standard) |
| Noticeable noise improvement | 6mm toughened |
| Significant noise reduction (road, rail, neighbours) | 6.4mm Stadip Silence |
| Maximum noise reduction | 6.8mm Stadip Silence or 10.8mm Ultra-Panel |
| Thermal improvement, lower bills, EPC rating | 4mm or 6mm Low-E |
| Both noise and thermal improvement | Discuss with us — options are available |
| Commercial application | Vision HD Hinged with 28mm DGU |
If you’re unsure, we’re happy to advise before you order. Most customers come to us with a noise or thermal goal in mind; we match the glass specification to that goal. For secondary glazing for listed buildings or conservation area properties, the right glass choice will also take planning constraints into account.
FAQs
What is the best glass for secondary glazing soundproofing?
For serious noise reduction, Stadip Silence PVB acoustic laminate in 6.4mm or 6.8mm specification is the strongest option, delivering 51 to 53dB sound reduction. 6mm toughened glass gives 49dB+ and is a good middle-ground choice. The glass type is only part of the equation — the air gap between the secondary unit and the primary window also matters. A 100mm minimum gap, ideally 150 to 200mm, is recommended for acoustic performance.
Does Low-E glass improve noise reduction in secondary glazing?
Low-E glass is a thermal upgrade, not an acoustic one. The hard coating improves thermal performance but does not significantly change the dB performance of the panel. For both thermal and acoustic improvement, it’s possible to specify a Low-E glass in combination with acoustic performance, depending on which product and configuration you choose.
What is acoustic laminate glass and how does it work?
Acoustic laminate glass uses a PVB interlayer bonded between two panes of glass. When sound energy passes through the glass, the PVB layer absorbs and dissipates it, particularly at mid-to-high frequencies that standard glass lets through relatively easily. The result is significantly better noise reduction compared to a single pane of the same thickness.
Can I order different glass types on different panels?
Yes. If you have a particularly noisy room and want acoustic glass there, while choosing standard glass for other windows, we can accommodate that during the ordering process.
Is toughened glass safe for secondary glazing panels?
Yes. Toughened glass is the safety standard for glazed panels in domestic and commercial settings. If it breaks, it fractures into small, blunt fragments rather than sharp shards. Clearview uses toughened glass as the standard specification and upgrades to toughened acoustic laminate or Low-E glass as required.
