Low-E / Energy Glass
Low-emissivity coatings reflecting infrared heat back into the room. Reduces emissivity from 0.84 to as low as 0.01. The single most effective upgrade for thermal performance.
Low-E — Thermal Performance
Low-E is the single most effective upgrade for sealed unit thermal performance — reducing U-value from 2.8 to 1.1 W/m²K (a 61% improvement in a standard DGU). Low-E is now the default for virtually all residential and commercial sealed unit production.
Complete Brand Reference
| Manufacturer | Product | Type | Emissivity | U-Value* | Toughenable |
|---|---|---|---|---|---|
| Pilkington | Optitherm™ S3 | Soft coat | 0.03 | 1.0 | No (pre-coat) |
| Pilkington | K Glass™ S | Soft coat | 0.05 | 1.1 | Yes |
| Pilkington | Optitherm™ S1+ | Hard coat | 0.15 | 1.5 | Yes |
| Saint-Gobain | Planitherm® Total+ | Soft coat | 0.03 | 1.0 | No |
| Saint-Gobain | Planitherm® Ultra N | Soft coat | 0.03 | 1.0 | No |
| Saint-Gobain | Eclaz® | Soft coat | 0.03 | 1.0 | No |
| Guardian | ClimaGuard® Premium2 | Soft coat | 0.03 | 1.0 | No |
| AGC | iplus Top 1.1 | Soft coat | 0.03 | 1.1 | Available |
*Centre-pane U-value in 4-16-4 DGU with argon.
Coating Position
Surfaces numbered 1-4 outside to inside. Position determines function:
- Surface 3 (standard): Inner pane cavity face — reflects room heat back inside. Default for all residential/commercial.
- Surface 2 (solar): Outer pane cavity face — reflects solar heat outward. For overheating control.
- Surfaces 2+5 (TGU): Dual Low-E for maximum triple glazing performance — U-values to 0.5.
See how the coating keeps room heat in while letting daylight through:
Soft Coat vs Hard Coat
| Emissivity | Typical U-Value* | Appearance | Best Fit | |
|---|---|---|---|---|
| Soft Coat (sputtered) | 0.02-0.05 | 1.0-1.1 | Neutral, virtually invisible | Standard for all new sealed units |
| Hard Coat (pyrolytic / K Glass) | 0.15-0.20 | 1.5-1.6 | Very slight tint, more durable surface | Secondary glazing, single-pane upgrades, exposed edges |
*Centre-pane U-value, 4-16-4 DGU with argon fill.
Where Each Fits
Soft coat is the default specification for virtually every new residential and commercial sealed unit — it delivers the lowest emissivity and the best U-value, and once built into a sealed unit its unprotected surface faces into the argon-filled cavity, safe from handling and weathering. Hard coat trades some thermal performance for a coating that can be left exposed — useful on secondary glazing panels, single-glazed upgrades, or heritage sash refurbishments where a full DGU replacement is not an option but a thermal improvement still is.
Pairing with Argon and Warm Edge
Low-E does the majority of the work, but centre-pane U-value only tells part of the story. An argon gas fill in the cavity reduces convective heat transfer between the panes, typically improving on an air-filled equivalent. A warm edge spacer cuts the thermal bridge at the perimeter of the unit, where a standard aluminium spacer would otherwise undermine the centre-pane figure. Low-E, argon and warm edge together — rather than any one in isolation — is what gets a whole-window U-value down to the level needed for demanding Part L specifications.
Calculating Whole-Unit Performance
Centre-pane U-values are a useful comparison point between products, but the figure that matters for Building Regs and WER ratings is the whole-window U-value, which also accounts for the frame and spacer. Use the U-value calculator to work out a whole-unit figure for a specific glass and frame combination, and see the Building Regs guide for current Part L and WER context.
Related Products & Glass Types
Common Questions
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