The coefficient that indicates the thermal insulation of a glass pane is the thermal transmittance coefficient, expressed as Ug. The Ug of a glass pane shows the amount of energy passing through the double or triple glazing per unit of time, per unit of area, per unit of temperature difference. The values for the Ug (glass) Thermal Transmittance Coefficient are given in w/m2K. The smaller this number, the better.
The terminology and how energy-efficient glass works are given in detail.
