A value for the glazing
Ug describes thermal transmittance at the centre of the glazing. Expressed in W/(m²·K), it indicates how readily heat passes through that part of the glass assembly. Lower values indicate better insulation.
Keep the scope clear
The Ug value excludes the frame and the additional heat transfer around the glass edge. Use Uw when comparing complete windows, and retain Ug when describing the glazing itself.
Read the glass specification
Request the full glass build-up with the declared value. Keep thermal insulation, daylight and solar-control information together when reviewing options, so a single figure does not become the entire design brief.
