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Reduced heat loss

Low-E glass for a warmer glazing assembly

Specify a complete sealed-unit requirement or a coated pane for fabrication, with the frame depth and desired thermal performance recorded.

Product guide

Low-E glass for a warmer glazing assembly

Specify a complete sealed-unit requirement or a coated pane for fabrication, with the frame depth and desired thermal performance recorded.

Clear window glazing in a comfortable living-room concept.
AI-generated illustration. Appearance varies by specification; this is not an exact product sample.

Low-E glass, low-emissivity glazing and thermal-insulation glass

Low-emissivity glass uses a coating as part of a glazing specification intended to limit heat transfer. Its performance is assessed in a particular construction. The coating, pane arrangement, cavities, gas and frame all influence what a complete window or glazed unit can achieve.

Hard-coat and soft-coat products have different processing and installation requirements. Ask for the named coating, the intended coated surface and the supplier's proposed glass build. A coating should not be selected from appearance alone.

A centre-pane Ug value describes glass under stated conditions; it is different from a whole-window or whole-product U-value. Record which value your project specification requires. Low-E, solar control and acoustic performance are different functions even where they are combined in one unit.

Low-E glass for a warmer glazing assembly for your project

Common enquiry briefs include replacement sealed units, new windows, roof glazing, pane for fabrication. Describe the intended use and the supporting construction so the supplier can assess the complete specification. Different applications can need different glass processing, fixings and installation details.

Read the correct U-value

A lower Ug describes reduced centre-pane heat transfer. It is not the Uw of the full window.

Choose the complete build

Pane selection, gas and cavity all contribute. The same coating can appear in different assemblies.

What to include in a made-to-measure quote

Compare quotes using the same dimensions, quantities, finish, glass construction and installation scope. If you have a drawing or an existing specification, include its reference and identify which details still need advice.

  • How will it be glazed?: The complete assembly determines the performance.
  • Coating request: A supplier must select a product compatible with the processing and surface position.
  • Thermal requirement: Ug is centre-pane performance; Uw describes the complete window.
  • Safety processing: Coated products may have separate toughenable variants.

Cut-to-size dimensions, edges and fabrication

Measure the finished glass only when the fitting allowances and support details are known. Otherwise identify the opening or existing panel you measured and request a survey. Give each different size its own basket line, with its quantity and drawing reference.

Holes, cut-outs, shaped edges and interfaces with hardware should be settled before manufacture. The finished glass construction and any coatings must suit the intended environment. A screen preview or concept photograph cannot replace a sample, survey or product-specific installation drawing.

Supplier checks before manufacture

  • Use performance for the exact pane/cavity/gas build, not for the coating in isolation.
  • Confirm coating surface, edge deletion and processing with the manufacturer or fabricator.

Requesting comparable glass quotes

Save the choices you know and ask for help with the rest. The quote basket records a specification request rather than placing a manufacturing order. A firm quote needs an agreed final build, dimensions, delivery arrangements and any installation or design work.

When comparing proposals, check that glass-only supply and supply with fitting cover the same scope. Ask who provides measurement, drawings, supports, compatible hardware, lifting access and finishing work. Keep the final approved specification with the order.

Sources and further reading

Configure your glass ↓Help me chooseSee the research

Guided specification · Save multiple sizes · Supplier-confirmed quotes

Your glass, step by step

Build your specification

Choose what you know. Leave the rest for a supplier to advise. Add different sizes as separate basket lines.

No account needed to configure
1. Your project

1What are you making?

2. Glass and performance

2Choose the details

Examples and guidanceLow-emissivity coating and glazing surface

The complete assembly determines the performance.

Example cavity-facing low-E coatingDouble-glazed example with thin coating on a cavity-facing surface of the inner pane. Confirm permitted surface with manufacturer.How will it be glazed?Illustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

A low-emissivity coating changes radiant heat transfer at a glass surface. It is a thin surface treatment, not another glass pane. Confirm the named coating and its permitted position in the proposed glazing.

The diagram is one double-glazed example with a cavity-facing coating, not a placement rule for every coated product. Number surfaces from outdoors to indoors and obtain the manufacturer’s approved construction. Centre-pane Ug differs from whole-window Uw.

Examples you may seeSpecify the named coating and intended build-up.Ask whether a quoted thermal value applies to the glass unit or the whole window.Available choices: Help me choose; Single pane; Double-glazed unit; Triple-glazed unit; Secondary glazing.Current choice: Help me choose. This is your request for the supplier to confirm.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Pilkington: Optitherm low-emissivity glass (opens in a new tab) ↗

The complete assembly determines the performance.

Examples and guidanceLow-emissivity coating and glazing surface

A supplier must select a product compatible with the processing and surface position.

Example cavity-facing low-E coatingDouble-glazed example with thin coating on a cavity-facing surface of the inner pane. Confirm permitted surface with manufacturer.Coating requestIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

A low-emissivity coating changes radiant heat transfer at a glass surface. It is a thin surface treatment, not another glass pane. Confirm the named coating and its permitted position in the proposed glazing.

The diagram is one double-glazed example with a cavity-facing coating, not a placement rule for every coated product. Number surfaces from outdoors to indoors and obtain the manufacturer’s approved construction. Centre-pane Ug differs from whole-window Uw.

Examples you may seeSpecify the named coating and intended build-up.Ask whether a quoted thermal value applies to the glass unit or the whole window.Available choices: Help me choose; Soft-coat low-E; Hard-coat low-E; Match a named product — see notes.Current choice: Help me choose. This is your request for the supplier to confirm.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Pilkington: Optitherm low-emissivity glass (opens in a new tab) ↗

A supplier must select a product compatible with the processing and surface position.

Examples and guidanceLow-emissivity coating and glazing surface

Ug is centre-pane performance; Uw describes the complete window.

Example cavity-facing low-E coatingDouble-glazed example with thin coating on a cavity-facing surface of the inner pane. Confirm permitted surface with manufacturer.Thermal requirementIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

A low-emissivity coating changes radiant heat transfer at a glass surface. It is a thin surface treatment, not another glass pane. Confirm the named coating and its permitted position in the proposed glazing.

The diagram is one double-glazed example with a cavity-facing coating, not a placement rule for every coated product. Number surfaces from outdoors to indoors and obtain the manufacturer’s approved construction. Centre-pane Ug differs from whole-window Uw.

Examples you may seeSpecify the named coating and intended build-up.Ask whether a quoted thermal value applies to the glass unit or the whole window.Available choices: Help me choose; Improve an existing unit; Ug target in project specification; Whole-window Uw target — frame details to follow.Current choice: Help me choose. This is your request for the supplier to confirm.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Pilkington: Optitherm low-emissivity glass (opens in a new tab) ↗

Ug is centre-pane performance; Uw describes the complete window.

Examples and guidanceSingle-pane glass thickness and processing

Coated products may have separate toughenable variants.

Monolithic glass sectionOne solid glass pane with thickness measured between its two faces.Safety processingIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

A monolithic pane is one piece of glass. Its thickness is measured between its two faces; toughening changes the glass’s stress state rather than adding a separate layer.

The suitable thickness depends on use, size and support. Specify safety requirements separately. Cutting, drilling and edge preparation must be agreed before any toughening; finished toughened glass cannot be recut.

Examples you may seeAn 8 mm request describes the single pane, subject to supplier confirmation.A supported furniture panel and an unsupported span need different design checks.Available choices: Help me choose; Annealed — suitability to confirm; Toughened; Laminated; Overhead build — specialist review.Current choice: Help me choose. This is your request for the supplier to confirm.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗

Coated products may have separate toughenable variants.

3. Sizes and fabrication notes

3Size and quantity

Enter finished glass sizes. If you only have opening sizes, ask for a survey or fitting allowance before ordering.

Examples and guidancePanel outline and drawing

Choose the finished outline. A rectangle needs width and height; a circle needs diameter. Bespoke shapes need enough dimensions, radii and datum references to define the outline.

Panel dimension referenceFinished rectangular panel width and height. Opening dimensions are a different reference.ShapeIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

A preview is an illustration; ask the supplier to confirm the manufacturing drawing or template.

Examples you may seeRectangle or square: finished width and height.Circle: diameter, with hole or cut-out positions separately documented.Available choices: Rectangle; Circle; Shaped / drawing to follow.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗
Examples and guidanceMeasurement units

1 cm equals 10 mm. Choose the units before entering sizes; keep drawing annotations in the same units.

Panel dimension referenceFinished rectangular panel width and height. Opening dimensions are a different reference.Measurement unitsIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

The form converts entered measurements to the existing millimetre specification fields.

Examples you may see120 cm = 1,200 mm.60 cm = 600 mm.Available choices: Millimetres (mm); Centimetres (cm).Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗
Examples and guidanceFinished panel dimensions

Record the finished width and height of each distinct panel. For a circle use its diameter; shaped work needs a dimensioned drawing or agreed template.

Panel dimension referenceFinished rectangular panel width and height. Opening dimensions are a different reference.Width ( mm )Illustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

An opening, frame and finished glass are different references. Request a survey when the finished manufacturing dimensions remain unknown.

Examples you may seeOne size per basket line; quantity records identical pieces.Check units and the dimension reference before confirming manufacture.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗
Examples and guidanceFinished panel dimensions

Record the finished width and height of each distinct panel. For a circle use its diameter; shaped work needs a dimensioned drawing or agreed template.

Panel dimension referenceFinished rectangular panel width and height. Opening dimensions are a different reference.Height ( mm )Illustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

An opening, frame and finished glass are different references. Request a survey when the finished manufacturing dimensions remain unknown.

Examples you may seeOne size per basket line; quantity records identical pieces.Check units and the dimension reference before confirming manufacture.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗
Examples and guidanceQuantity of identical pieces

Quantity counts pieces with the same size and specification. Enter different sizes or constructions as separate basket lines so each requirement is retained.

Numbered specification scheduleA numbered schedule separates panel specification, hardware, delivery, fitting and approvals.QuantityIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

Examples you may seeThree identical panels: quantity 3.Two distinct sizes: separate lines.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗
Examples and guidanceDrawing references and unresolved details

Record drawing references, site conditions and requirements not captured in the choices. Identify anything that needs a survey or supplier confirmation before manufacture.

Numbered specification scheduleA numbered schedule separates panel specification, hardware, delivery, fitting and approvals.Project and fabrication notesIllustrative schematic, not to scale or a fabrication / fixing specification.

What your choice means

Examples you may seeNumber drawings and panel positions consistently.State access constraints and the requested work scope.Low-E glass for a warmer glazing assembly: original Flow application conceptAI-generated product illustration from Google Flow; not an exact product sample, completed installation or proof of performance.Guardian: glass types (opens in a new tab) ↗

0/2000 characters. Share drawings and photos in the job conversation after submitting.

Before you choose

The decisions that matter

01

Read the correct U-value

A lower Ug describes reduced centre-pane heat transfer. It is not the Uw of the full window.

02

Choose the complete build

Pane selection, gas and cavity all contribute. The same coating can appear in different assemblies.

Ready for a useful supplier quote

  • Use performance for the exact pane/cavity/gas build, not for the coating in isolation.
  • Confirm coating surface, edge deletion and processing with the manufacturer or fabricator.
Compare complete sealed-unit builds →

Research behind these choices

Reviewed 23 October 2026. Manufacturer guidance and supplier ordering pages inform these design questions. Agree the final construction and project requirements with your supplier.

Reference performance data

Existing Pilkington Spectrum reference data for named builds. Values apply only to the listed construction; these rows are not results for your selection above. NPD means no declared value in this dataset.

Certified double-glazed units with K Glass / Optitherm low-E

Certified double-glazed units with K Glass / Optitherm low-E
Reference build / glassU / Ug (W/m²K)Light (%)g-valueRw (C; Ctr), dB
Optitherm S1 Plus HST 6mm / 28argon-15air-16argon / Eclipse Advantage Grey HST 6mm0.5150.23NPD
Optiphon Laminated 10.8mm / 24argon-16argon / K Glass S HST 8mm0.7380.47NPD
Suncool Optilam Blue 50/27 Laminated 9.1mm / 14argon-16argon / K Glass T 8mm0.7220.2NPD
AviSafe 12mm / 11krypton-16argon / K Glass S T 10mm0.7410.45NPD
AviSafe Heat strengthened 4mm / 22krypton-16argon / K Glass A HST 6mm0.7600.59NPD
Optifloat Clear 2mm / 17argon-17argon-16argon / K Glass S 4mm0.7700.62NPD
Optifloat Clear 2mm / 18argon-18argon-16argon / K Glass S 4mm0.7700.62NPD
Optifloat Clear 2mm / 20argon-20argon-16argon / K Glass S 4mm0.7700.62NPD
Optifloat Clear 2mm / 22argon-22argon-16argon / K Glass S 4mm0.7700.62NPD
Optifloat Clear 2mm / 24argon-24argon-16argon / K Glass S 4mm0.7700.62NPD

Useful questions

Can I get a quote before I know every detail?

Yes. Choose Help me choose where you need advice, or request a site measurement. Suppliers can review the brief; a firm manufacturing price needs an agreed final specification.

Does adding a panel place an order?

No. It saves a specification in your quote basket. Review the basket and provide your delivery details to request supplier quotes. Your configuration does not approve the product for installation.

What should I confirm for low-e coated glass?

Use performance for the exact pane/cavity/gas build, not for the coating in isolation. Confirm coating surface, edge deletion and processing with the manufacturer or fabricator.

Compare related glass

Insulating glass units (IGU / DGU / TGU) →Solar control glass →Self-cleaning glass →