The stadium is referred to as the "bird's Nest" because of its saddle-shaped steel roof and interwoven façade. The roof measures 330m long by 220m wide and weighs a total of 45,000 tones. Its upper surface is clad with ethylene tetra fluoro ethylene(ETFE) panels which let in natural light and its lower surface has an acoustic membrane which reflects and absorbs sound. This maintains the atmosphere in the stadium.
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