INSULATION PERFORMANCE OF GLAZING
As shown in the diagram to the right, the following units have a successively increasing thermal performance (U values in brackets are imperial measurements):

A SINGLE GLAZING - no longer recommended for most climates. U-value 6.24(1.1).

B CLEAR DOUBLE-GLAZING - this is a sealed factory unit with airspace - known as insulating glass because of its good insulating characteristics. U-value 2.78(0.49)

C CLEAR DOUBLE-GLAZING - LOW-E - a transparent metallic (low emissivity) coating reflects heat back to occupied space. U-value 1.93(0.34)

D CLEAR DOUBLE-GLAZING - LOW-E - GAS FILLED - uses Argon or Krypton gazes - less conductive than air within the cavity. U-value 1.59(0.28)

E CLEAR TRIPLE-GLAZING - in many cases equivalent to D. If gazes and metallic coating are used, then performance is increased further. U-value 1.59(0.28)

F MULTIPLE COMPARTMENT - SUSPENDED FILMS - uses two panes of glass with two, low-E coated polyester films - very high performance.. U-value 0.74(0.13)

DISADVANTAGES - with the exception of some proprietary F systems, the above-noted solutions, using clear glazing, do very little to limit solar heat gain.

SOLAR HEAT GAIN PERFORMANCE OF GLAZING

G TINTED OUTER PANE - energy absorbing materials are dispersed throughout the pane, giving it a tint of varying colour and intensity with the ability to reduce energy penetration.

H REFLECTIVE COATINGS - added to the No. 2 surface reflect rather than absorb solar radiation, thus reducing overall solar heat gain.

DISADVANTAGES - both methods G and H, although effective for reducing solar heat gain, may limit daylighting potential. Spaces are typically "dark"; views to the outdoors are may be subdued; and the quality and colour of naturally available daylight may be altered.