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Low-E coated glass — the metallic-oxide layer that drops U-value by 30%
Low-emissivity (low-E) glass is the single biggest thermal upgrade you can specify in a sealed unit. A microscopically thin coating of metallic oxide — typically tin oxide (hard-coat) or layered silver (soft-coat) — reflects long-wave infrared back into the room while letting short-wave solar gain pass through. The result: U-values dropping from around 2.7 W/m²K on an uncoated unit to 1.1-1.4 W/m²K on a single-coated low-E unit, and as low as 0.5 W/m²K on a dual-coated triple. Pane Relief stocks Pilkington K Glass, Saint-Gobain Planitherm Total+, Guardian ClimaGuard, and AGC Optitherm — pick your coating type below.
Upgrading misted or under-performing glass
If your existing units are 15+ years old, they almost certainly have no low-E coating — that's why your radiators run all winter. A like-for-like swap to soft-coat low-E typically cuts U-value by half and pays back through heating-bill savings inside 5-7 years. Free spec advice on the helpline, 10-year edge-seal warranty, FENSA installer recommendations in your postcode.
Configure my low-E unitSpecifier, installer, builder
Net 30 trade accounts, tiered discount on 5+/20+/50+ unit orders, BS EN 1279-5 Declaration of Performance and coating data sheets (emissivity, light transmittance, solar factor) shipped with every order on request. Pilkington, Saint-Gobain, Guardian, and AGC coatings stocked. Bespoke quotes via the trade portal.
Trade pricing & bulk ordersWhich low-E coating do you need?
Hard-coat, soft-coat, dual-low-E triple, or solar-control variants. Pick the closest match for your project — performance and price step up across the range.
Hard-coat (Pilkington K)
Pyrolytic tin-oxide coating fused at float. Robust, tougher edge, easier to handle — U=1.6-1.9 W/m²K in a standard 4-16-4 argon unit.
Soft-coat (Planitherm / Optitherm)
Magnetron-sputtered silver layers. Lower emissivity, higher light transmittance — U=1.1-1.3 W/m²K. Must sit on a protected face inside the sealed unit.
Dual low-E triple
Low-E coating on both inner faces of a triple-glazed unit. Krypton-filled cavities. Targets U=0.6-0.8 — Passivhaus territory.
Solar-control low-E
SunGuard, Cool-Lite, or Solar-E variants. Low solar factor (g-value 0.3-0.4) — cuts overheating in south-facing or roof-glazed openings.
Low-E + toughened
Low-E coating combined with BS EN 12150 safety glass. For doors, low-level glazing, or critical locations within 1500mm of floor.
Full A-rated build
Low-E + argon + warm-edge spacer — the spec that hits BFRC A under WER. See the A-rated collection for finished products.
How low-E coatings actually work
A 1-page explainer so you can specify with confidence — coating side, gas fill, and warm-edge spacer all matter.
The 5-point coating brief
- Coating chemistry: hard-coat is pyrolytic tin oxide bonded at the float-line; soft-coat is sputtered silver applied off-line. Silver gives lower emissivity (better U-value) but oxidises if exposed.
- Coating face: soft-coat must sit on face 2 or face 3 — inside the sealed unit. Hard-coat is durable enough to sit on face 4 (room-side) if needed.
- Gas fill: argon is standard and adds ~10% U-value improvement vs air. Krypton (in slim or triple-glazed units) adds another 15-20%.
- Spacer bar: warm-edge (Swisspacer, Super Spacer, Edgetech Super Spacer TriSeal) cuts edge heat-loss versus aluminium by 50-65%, and is mandatory for BFRC A.
- Full unit U-value = centre-pane U + edge effect + frame contribution. The collection prices reflect the glass unit; full window-WER ratings depend on frame and installation.
Pricing & what's in the box
Prices on this collection are "From £X" at the smallest stock size with standard 4-16-4 argon-filled hard-coat low-E. Soft-coat, dual-low-E, krypton fill, warm-edge spacer, and toughened safety glass are priced live in the configurator. Every unit ships with the coating data sheet on request — emissivity, light transmittance, solar factor (g), and U-value.
Low-E glass — common questions answered
Q: Hard-coat or soft-coat — which should I order?
For most replacement jobs, soft-coat (Planitherm Total+ or Optitherm) is the right answer — emissivity of about 0.03-0.05 versus 0.15-0.17 on hard-coat means a noticeably lower U-value (1.1 W/m²K vs 1.6 W/m²K in a standard 4-16-4 argon unit). Hard-coat (Pilkington K) is worth specifying where the coating may end up on a room-facing surface, where the glass needs to be heat-treated after coating, or for very budget-sensitive jobs.
Q: Will the coating tint or change the appearance of the glass?
Subtly, yes. Hard-coat low-E has a very faint yellow-bronze cast (most people don't notice). Soft-coat has a slightly cooler, neutral-grey reflection from outside and a marginal drop in visible light transmittance (LT around 78-80% on a clear-soft-coat versus 89-90% on plain float). Dual-low-E triples reflect more from outside in low-light — this is normal and expected, not a fault.
Q: Does low-E hurt solar gain — won't my house be colder in winter?
The opposite. Standard low-E coatings are tuned to be spectrally selective: they reflect long-wave infrared (room heat) back inwards while letting short-wave solar infrared (sunshine) pass through. Net effect in a UK climate: lower heat loss without losing the free passive solar gain. The g-value (solar factor) on a clear low-E is typically 0.55-0.65 — only solar-control low-E variants intentionally cut g-value to 0.3-0.4 for overheating-prone openings.
Q: How can I tell if my existing glass has a low-E coating?
The flame test: hold a lighter or match a few inches from the glass and count the reflections. Standard glass shows four reflections all the same colour. Low-E glass shows one reflection in a different colour (slightly pink, copper, or violet) — that's the coating. Alternatively, send us a close-up photo of any kitemark or etched stamp on the edge — most modern units carry a code identifying the coating.
Q: How much will swapping to low-E actually save on heating bills?
Depends on baseline. Replacing 1990s-era uncoated double glazing (U around 2.7-3.0 W/m²K) with modern low-E argon (U around 1.2 W/m²K) typically cuts whole-house heat loss through glazing by 55-60%. In a semi-detached 1980s house with eight medium-sized windows, that's an annual saving in the region of £120-£220 at 2026 gas prices — payback inside 7-10 years on the glass-only spend, faster if you also enable smart heating controls.
Q: Can low-E be combined with acoustic or laminated specs?
Yes — the coating sits on one face of one pane, so the other pane can be a laminated acoustic interlayer (Pilkington Optiphon, Saint-Gobain Stadip Silence) without conflict. Common high-spec mix: 6.4mm acoustic laminated outer + 16mm argon + 4mm soft-coat low-E inner. U-value 1.2 W/m²K, Rw 38-42 dB. Configure it on the unit page.
Q: Does the coating wear out or degrade over time?
No — provided the sealed unit stays sealed. Soft-coat silver oxidises only when exposed to atmospheric moisture; sitting on the protected internal face of an argon-filled cavity, it's chemically stable for the design life of the unit (BS EN 1279-2 weathered durability: 25-30 years on a quality unit). Coating performance is warrantied 5 years; edge-seal integrity warrantied 10 years.
Q: Will Building Control accept a low-E retrofit?
For glass-only replacement of an existing window, no Building Control notification is required (it's a like-for-like maintenance job). For whole-window or new-build, Approved Document L (Conservation of Fuel and Power) requires a U-value of 1.4 W/m²K or better — a standard soft-coat low-E argon unit clears that with margin. For Passivhaus or EnerPHit projects you'll need a dual-low-E triple (see the Passive House triple-glazing collection).
Q: What about sun-load in a south-facing conservatory or roof window?
For overheating-prone openings — south or west-facing conservatories, lantern roofs, large picture windows — specify a solar-control low-E (Pilkington Suncool, Saint-Gobain Cool-Lite, AGC Stopray). These cut the g-value to around 0.30-0.40 so less solar heat passes through, while still giving a 1.0-1.2 W/m²K U-value. Trade-off: slightly cooler-toned reflection from outside. See the energy-rated glass guide for the full spec ladder.
Q: What's the lead time?
Stock-size soft-coat low-E units: 5-7 working days. Custom rectangular: 7-10 working days. Dual-low-E triples and krypton-filled: 10-14 working days. Solar-control or specialist coatings (SunGuard, Cool-Lite): 12-16 working days. Toughened or laminated low-E adds 2-3 working days.
Related guides and specifications
Need help picking the right low-E coating?
Call the helpline on 0117 330 3057 (08:00-18:00 Mon-Fri), or request a quote. Trade accounts unlock live tier pricing and Net 30 terms.