Absorptance. The ratio of radiant energy absorbed to total incident radiant energy in a glazing system.
Acrylic. A thermoplastic with good weather resistance, shatter resistance, and optical clarity, used for glazing.
Aerogel. A microporous, transparent silicate foam used as a glazing cavity fill material, offering possible U-values below 0.10 BTU/(h-sq ft-°F) or 0.56 W/(sq m-°C).
Air infiltration. The amount of air leaking in and out of a building through cracks in walls, windows and doors.
Air-leakage (air infiltration).The amount of air leaking in and out of a building through cracks in walls, windows, and doors.
Air-leakage rating. A measure of the rate of air-leakage around a window, door, or skylight in the presence of a specific pressure difference. It is expressed in units of cubic feet per minute per square foot of frame area (cfm/sq ft). Formerly expressed as cubic feet per minute per foot of window perimeter length (cfm/ft) but not now in use. The lower a window's air-leakage rating, the better its airtightness.
Annealed glass. Standard sheet of float glass which has not been heat-treated.
Annealing. Heating above the critical or recrystallization temperature, then controlled cooling of metal, glass, or other materials to eliminate the effects of cold-working, relieve internal stresses, or improve strength, ductility, or other properties.
ANSI. American National Standards Institute. Clearing house for all types of standards and specifications.
Argon. An inert, nontoxic gas used in insulating glass units to reduce heat transfer.
ASHRAE. American Society of Heating, Refrigerating and Air Conditioning Engineers.
ASTM. American Society for Testing and Materials. Organization that sets standards for testing of materials.
Awning. Window similar to a casement except the sash is hinged at the top and always swings out.