Acoustic Glass Thicknesses Compared
Glass specification is where most of the acoustic budget goes, and it is where the most money is wasted. Thicker is not automatically better, laminate is not the same as thickness, and the right answer depends on what your original pane is already doing.
4mm toughened float
The baseline. It is the standard specification where the goal is draught proofing, warmth or condensation control rather than noise. It is light, it is inexpensive, and in a deep cavity it still delivers a worthwhile acoustic improvement simply by adding a second sealed layer. If your original glass is 3mm, a 4mm secondary pane is already asymmetric, which helps.
6.4mm acoustic laminated
Two panes of 3mm bonded with an acoustic PVB interlayer. This is the workhorse for domestic noise problems. The interlayer damps the pane so it does not resonate, and the thickness is clearly different from typical original glass. For most road noise, rail noise at moderate distance and general urban noise, this is the specification that gives the best result per pound.
- Best value acoustic option for most homes
- Damped rather than merely heavier
- Manageable weight for standard hardware
- Adds safety glass benefits as a bonus
6.8mm acoustic laminated
The same construction with a thicker interlayer, giving slightly better damping across the mid frequencies. The uplift over 6.4mm is real but modest, and it is worth taking where the noise source is close or persistent, such as a house fronting a main road or within a few hundred metres of a railway. It remains within the weight range that most sliders and hinged units handle comfortably.
8.8mm and 10.8mm laminated
Heavier laminated build ups used where the noise level is genuinely severe, on flight paths, alongside main lines, or on nightlife frontages. The gains are real at the lower frequencies but they arrive with consequences: heavier sashes need upgraded rollers or balances, frames need stiffer sections, and cost rises steeply. We specify these where the survey justifies them, not as a default.
12.8mm and beyond
This territory belongs to commercial and specialist projects with a stated acoustic target, typically driven by a planning condition or an acoustic report. At this weight the system design changes: lift out panels may become impractical, hinged units need heavy duty hardware, and the fixing detail into the reveal has to carry real load. It is engineering rather than shopping.
Why mismatching matters more than maximising
Two panes of identical thickness share a coincidence frequency, a band where both become acoustically weak. Deliberately choosing a secondary pane that differs from your original glass fills that gap. This is why a 6.4mm laminate behind original 3mm crown glass often outperforms a thicker pane chosen without reference to the existing window. Tell your installer what the original glass is, or ask them to measure it.
Where the money is better spent
If you have a choice between upgrading from 6.4mm to 8.8mm glass and increasing the cavity from 60mm to 120mm, take the cavity every time. Separation outperforms mass across the frequencies that matter for traffic and rail. Glass upgrades are the second lever, not the first.
Frequently asked questions
No. Toughened is a single heat treated pane. Laminated is two panes bonded around an interlayer, which is what provides acoustic damping.
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