The facade panels will form eight tall triangles of glass and steel, which grow alternately wider and narrower as they approach the top of the building. David M. Childs designed the tower’s glimmering exterior to refract light and change its appearance depending on the weather and the viewer’s position.

The first 20 floors of the building, which include the lobby and mechanical space, will have a more porous facade made of prismatic glass and an aluminum screen.

Construction workers at the World Trade Center site were said they were impressed by the first glimpse of the building’s future skin this week.

“Officially, I’m not allowed to have a comment,” said one worker who is helping build One World Trade Center. “Unofficially, I think it looks sweet.”

“You can start to see the scope of the building,” another worker added. “You can see what it’s going to be.”