From a post at Wired NY:
From the March 2012 PANYNJ WTC Progress Report:
One World Trade Center’s Exterior
Shimmers with New Podium Wall Glass Panels
... Starting this month, the walls of the 186-foot-tall 1 WTC podium are being clad in vertical glass panels to create a dynamic exterior that will animate the ground level experience of the building for pedestrians.
More than 4,000 frosted glass fins, each measuring 13 feet 4 inches by two feet, are being specially created by the contractor Permasteelisa. The glass fins will attach to the exterior of the podium wall at varying angles to create a series of v-shaped wing effects along the building surface. In addition to its aesthetic appeal, the v-shaped glass cladding pattern will provide needed ventilation for the mechanical systems within the podium— including a 1.2-megawatt, next-generation fuel-cell plant housed above the lobby.
One WTC uses a new form of high- performance, low-emittance (low-E) glass coating technology on its glass panels to maximize sunlight and minimize heat gain within the building. This glass coating is also reflective, creating a shimmering effect on the building’s surface. In addition, the podium wall will use concealed energy-efficient LEDs to create a soft exterior glow.
The podium cladding installation is a critical element of 1 WTC’s aesthetic. The tower is scheduled to top off at 104 floors and 1,776 feet above street level (including its spire). Upon completion of its exterior structure this year, 1 WTC will be the tallest skyscraper in the United States ...
• The podium’s new glass panels reflect, refract, and transmit light much like the water cascading in the nearby memorial pools.
• The low-emittance (low-E) coatings on 1 WTC’s glass panels are microscopically thin layers of metal or metallic oxide that block the transfer of heat from sunlight through the window. Though made of metal, these layers are virtually invisible.