Warm Edge Spacers: How They Cut Heat Loss at the Edge

Ask where a sealed unit loses heat and most people point at the glass. In a modern low-E unit, the glass is actually the strong link — the weak one runs around the perimeter.

The cold bridge problem

Traditional spacer bars are aluminium, one of the most conductive materials in a building. The bar forms a continuous metal bridge from the warm inner pane to the cold outer pane, dumping heat around the edge of every unit. That cold perimeter is also where room-side condensation forms first — the tell-tale fogging strip around the glass edge on winter mornings.

What warm edge changes

Warm edge spacers replace the aluminium with composite or stainless-steel-and-polymer constructions that conduct a fraction of the heat. The linear heat loss at the edge (the psi value) drops sharply, edge-of-glass temperatures rise by several degrees, and condensation risk falls with them.

What it means in numbers

• Whole-window U-value typically improves by around 0.1–0.2 W/m²K
• Internal edge-of-glass temperature rises roughly 2–4°C in cold weather
• Condensation-free hours increase noticeably in kitchens and bathrooms

Specifying it

Warm edge adds little to the price of a unit and nothing to the fitting process. We fit it as standard across our range. If you are comparing build-ups, run both options through the U-value calculator — the edge detail moves the whole-window number more than most people expect.