Double glazing is a single window made from two glass panes separated by a sealed cavity, known formally as an Insulated Glass Unit, or IGU. The trapped air or inert gas (usually argon) dramatically reduces heat transfer compared to a single pane.
How an IGU is built
- Two glass panes are cut to size, typically 4 mm or 6 mm float.
- A perimeter spacer bar (usually aluminium or thermally-broken plastic) is bonded to one pane.
- The cavity inside the spacer is filled with desiccant to absorb residual moisture.
- The second pane is bonded to the spacer with a primary butyl seal, then a secondary structural seal (silicone or polysulfide) wraps the unit.
- For best thermal performance, the cavity is filled with argon gas (denser than air, lower conduction).
What it does well
- Thermal performance, typical IGU U-value is 2.7 W/m²K vs about 5.8 for single glazing. Combined with low-E coatings, this drops to ~1.6.
- Acoustic improvement, moderate, especially with asymmetric pane thicknesses (e.g. 6 mm + 4 mm).
- Condensation reduction, the inner pane stays warmer in winter, reducing condensation.
- Energy bills, the headline reason most owners upgrade. Heating and cooling load both drop.
Cavity options
| Cavity fill | Effect |
|---|---|
| Air (10 to 16 mm gap) | Standard. Good thermal improvement vs single glazing. |
| Argon | ~30% better thermal performance than air. Standard premium spec. |
| Krypton | Better again but expensive; used in narrow-cavity units. |
| Vacuum (VIG) | Highest performance, very thin profile. Newer technology. |
Low-E + IGU = the modern standard
Most modern double glazing pairs the IGU with a low-emissivity (low-E) coating on one of the internal pane surfaces. The coating reflects long-wave heat radiation back into the room (in winter) or out (in summer) without blocking visible light. More on low-E glass.
When double glazing is worth it
- New builds in the BASIX-required NSW climate zones
- Renovations where heating bills are high
- Bedrooms or living rooms on a busy road (use asymmetric panes for acoustic gain)
- North-facing rooms with large glazed areas in summer-hot climates (pair with low-E)
Frequently asked questions
Can existing single-pane windows be upgraded to double?
Usually no, IGUs are deeper than single panes and rarely fit existing frames. Most upgrades involve new frames designed for the IGU thickness.
Does double glazing block all outside noise?
It reduces noise but does not eliminate it. For serious acoustic performance, specify asymmetric pane thicknesses, laminated inner pane, and a wider cavity.
How long does an IGU last?
Quality IGUs are warranted for 10 to 15 years. Seal failure (signs: condensation inside the cavity) marks end-of-life and typically happens at 15 to 25 years.
Do you replace IGUs in existing frames?
Yes, failed IGUs can usually be replaced into the existing frame and beads. We measure, order a matching unit to spec, and swap in a single visit.
Get a quote
Need a quote? Call 02 4722 2787 or email sales@pantherglass.com.au with photos and we will come back the same business day.