Double vs triple vs vacuum glazing– all you need to know.

When you are choosing new aluminium windows, you’ll often see the thermal performance referenced with either double or triple glazing – like with our much-loved 58BW window system.

Both options improve comfort, reduce energy bills, and help create a quieter home—but understanding the differences can help you make the most informed choice.

Double Glazing

Double glazing is the UK industry standard. It features two panes of glass separated by a warm edge spacer bar and filled with an insulating gas layer (often argon). The standard thickness of the sealed unit is 28mm – with two 4mm panes of glass and a 20mm gap. This gap slows down heat transfer, helping to keep warmth inside during winter and heat out in summer, and reduces noise levels from outside.

It represents an excellent balance between cost and performance with U-Values of around 1.4 depending on the glass coating, spacer bar technology and type of gas, and works well to reduce condensation and improve comfort levels.

Triple Glazing

As the name suggests, triple glazing adds a third pane of glass in the centre, creating two insulating cavities. These sealed units can be up 44mm thick and, with two gaps, the heat transfer is reduced even further, and the acoustics improved a little more.

They tend to be marginally more expensive than double glazed units, but they can enhance overall energy performance with U-Values of around 1.0 and are often a good choice for colder regions or busy urban areas.

It’s worth bearing in mind though that triple glazing is heavier than double glazing so windows sometimes need stronger hinges, and, with three panes of glass, light transmission can be marginally reduced.

New generation options

There is also a new generation of sealed glass units on the horizon in the form of slimline triple glazing and vacuum glass.

These are mostly designed for retrofit applications where it can be difficult to fit standard sized glazing into existing frames. Slimline triple glazing uses thinner glass and narrower cavities which allow it to fit the same space as a double glazed unit, while vacuum glass does away with the gap altogether (replacing it with a vacuum between two panes) and lets a double glazed unit fit into a single glazed space.

Both offer exceptional levels of performance – vacuum glass, for example, can achieve U-Values a low as 0.5, but both are currently premium priced options and are primarily suited to sections of Heritage market where there are restrictions on replacing original frames with energy efficient aluminium upgrades.

Whether you choose double, triple, or the latest slimline or vacuum technologies, AluK’s range of windows and doors offer impressive energy efficiency and design flexibility. The right choice will depend on your home’s location, insulation goals, and architectural style.