The Port Authority of New York and New Jersey had spent about $6 million on the custom-made prismatic glass panels for the 1,776-foot skyscraper, which is slated to be the tallest in the U.S. when it is completed in late 2013.
But the glass bowed and broke during off-site testing and the agency decided to replace it in late March.
"It was a pragmatic decision," agency spokesman John Kelly said.
The change will not affect the project's budget or schedule. But it scraps a design created to allay concerns that the windowless base of the redesigned tower would look more like a bunker than an inviting office building.
The New York Police Department had raised security concerns about the original design for the building, previously dubbed the Freedom Tower, moving the building site several feet away from the street to make it more difficult for vehicles to approach it.
The 185-foot concrete base was added to the design in 2005 by architect David Childs.
But the base provoked concern about aesthetics. Critics said the concrete was uninviting and made the building look like a fortress.
Childs proposed the installation of the 2,000 prismatic glass panels, which reflect shimmering light and are more commonly used in shop windows and lamps. The glass came from a Pennsylvania company, was treated in China and then tested back in the United States. Builders had only ordered samples so far.
William M. Yanek, executive vice president of the Glass Association of North America, said he knew of no other building that used prismatic glass so extensively.
Kelly said the replacement material will be glass that is more typically used in construction, but the design is still being finalized.
"The design will be practical while being distinctive," Kelly said, adding that a key priority was staying within the budget.
Rick Bell, executive director of the American Institute of Architects New York chapter, said the site's iconic stature around the world made every detail of its construction important. He added that reconciling the security and aesthetic concerns was an almost unprecedented design challenge.
"The whole world is watching what we do and how we do it," Bell said.
Bell said he hoped the designers would seize the opportunity to incorporate public art or other creative elements in the base.
At the site, the steel frame is in place for 66 of an eventual 104 stories. The remainder of the building will also be covered in glass, some of which has been installed and is visible from surrounding streets. Plans call for 71 floors of office space along with retail shops, an observation deck and parking. Magazine publisher Conde Nast is among the companies in talks to lease space.
Another tower is under construction at the site, along with the Sept. 11 memorial and a transit hub. The memorial is scheduled to open on the 10th anniversary of the attacks this fall.
