As building materials go, straw generally gets a bad rap: A straw man is something that can be knocked over easily, and, as everyone knows, any decent wolf can blow down a straw house. But people have been building homes in the U.S. from straw bales encased in plaster or drywall since at least the 1890s, and the practice is experiencing something of a boom as more and more people recognize that it is an energy-efficient and eco-friendly way to build. Straw bales insulate so effectively that they can reduce energy costs by as much as 75 percent. Moreover, straw is a cheap, abundant waste product: As much as 200 million tons of straw are wasted or underused every year in the U.S. alone — enough to build about 4 million 2,000-square-foot buildings.