An insulated glass unit, or IGU, combines two or more panes separated by a sealed cavity. Its performance depends on the complete build-up: glass substrates, coatings, cavity width, gas, spacer, edge seal, pane processing and installation system.
Write the make-up from exterior to interior
A clear specification lists every component in order. For example: exterior tempered glass / spacer cavity with argon / interior laminated Low-E glass. Number the glass surfaces from outside to inside and identify the coating surface.
Do not write only ‘double glazing’ or ‘Low-E IGU’. These phrases do not define pane thicknesses, safety treatment, coating type, cavity, spacer or performance.
Select the glass substrates and processing
Each pane may be clear, ultra-clear, tinted, printed or coated. It may also be annealed, heat-strengthened, tempered or laminated depending on wind load, thermal stress, safety and post-breakage requirements.
Large façade units often need a structural review of both panes and the edge seal. See our curtain wall glass and window and door glass application pages.
Place the Low-E coating correctly
Low-E coatings reduce long-wave heat transfer and can also manage solar gain. Soft-coat products are normally protected inside the sealed cavity. The exact surface—commonly surface 2 or 3 in a double-glazed unit—depends on climate, desired solar performance, colour and coating product.
Confirm the coating manufacturer, product code, orientation and compatible processing. A visual mock-up can help evaluate exterior reflection and colour before mass production.
Define the cavity and edge system
- State the nominal cavity width.
- Identify air, argon or another fill gas and the required concentration.
- Define spacer type and colour.
- Confirm primary and secondary sealant compatibility.
- Consider altitude, climatic load, shipping route and installation conditions.
Use measurable performance targets
Specify U-value, solar heat gain coefficient or g-value, visible light transmission and exterior/interior reflectance using the required calculation method. If acoustics matter, define the weighted sound reduction target for the complete glazing assembly.
Published centre-of-glass values are not automatically the same as whole-window or whole-façade performance.
Reference the correct standard
GB/T 11944-2025 is the current Chinese product standard for insulating glass. GB/T 18915.2-2013 covers Low-E coated glass. Destination-market and contract requirements may add other standards, durability testing or certification.
A practical enquiry checklist
Send the make-up, dimensions, quantity, drawings, safety processing, coating code and surface, cavity, gas, spacer, sealant restrictions, performance values, standards, destination and packing requirements.
Explore our insulating glass capabilities or ask our team to review your IGU specification.