William LeBaron Jenney was the first engineer/architect who thought of using a skeleton to help construct taller buildings. Before his great idea, most buildings were built with really thick walls that helped the building stand up. New York's Woolworth Building, built in 1890, was 13 stories high and had walls almost 11 feet thick at ground level!
Today's buildings, thanks to skeletons, have much thinner walls. The steel beams are covered with a thin layer of CLADDING, which can be glass, metal, brick, stone, or some other material that is firmly fastened to the building to help keep the people inside warm in the winter, cool in the summer, and dry all year round.
CLADDING is like our SKIN and our CLOTHES. It is on the outside, helping keep us feeling great inside!