Explain simply why 168 stainless steel plates welded together is the correct answer to: Passage: Cloud Gate is a public sculpture by Indian-born British artist Sir Anish Kapoor, that is the centerpiece of AT&T Plaza at Millennium Park in the Loop community area of Chicago, Illinois. The sculpture and AT&T Plaza are located on top of Park Grill, between the Chase Promenade and McCormick Tribune Plaza & Ice Rink. Constructed between 2004 and 2006, the sculpture is nicknamed The Bean because of its shape. Made up of 168 stainless steel plates welded together, its highly polished exterior has no visible seams. It measures 33 by 66 by 42 feet (10 by 20 by 13 m), and weighs 110 short tons (100 t; 98 long tons).

Question: Based on this passage, what is the bean made of in chicago?. Explanation:
The important part for answering this question is: Made up of 168 stainless steel plates welded together, its highly polished exterior has no visible seams.