 Nearly 30 percent of structural steel used in the building consists of recycled steel . Rainwater is collected and used for irrigation of the park and to cool the building . Along with other sustainable design features , the building is designed to allow in plenty of natural light , power is metered to tenants to encourage them to conserve energy , the heating steam is reused to generate some power for the building , and recycled materials are used for insulation and interior materials . 
