In the 21st-century, the emphasis of curtain wall and slope wall manufacturers is on more highly weather resistant packages with heightened energy efficiency, using more durable and long-lasting materials and finishes, recyclable materials. Glass glazing, long thought to be a building's weak link with regard to energy performance, now rivals insulated walls in its ability to maintain a desired interior climate while reflecting unwanted effects of the sun. Today's walls are more sophisticated in every respect.

One PPG Place, Pittsburgh, PA John Burgee Architects with Phillip Johnson

"Today," says Carl Wagus, technical director for the American Architectural Manufacturers Association, "we are working on test methods for evaluating the performance of thermally broken aluminum-we've already developed a series of standards for evaluating thermal barriers structurally."

The movement to "green" architecture has meant that structural systems are being asked to support more material, including sun shades and light shelves. "Our systems are being tested structurally right now," says the director of the curtain wall division of one manufacturer. "Architectural firms say 40 percent of what they are designing right now has some type of sun shade built into the curtain wall system," says the source.

Radio Shack Corporate Headquarters Forth Worth, Texas Today, various curtain wall infill products can be used instead of glass. Aluminum panels, for example, were used on the Delphi Building.

"We take for granted in our industry that architects know what simple architectural framing systems are and what applications fit them best, but we get questions all the time that indicate otherwise," says the director of the curtain wall division of one manufacturer.