A growing number of U.S. companies are now offering homes built with three-dimensional, or 3D printing technology. The companies say 3D printers can build homes faster, for a lot less money, and in a much more environment friendly way than traditional building methods. They say the technology may also help solve America’s shortage of affordable housing. 3D printers make physical objects based on 3D models created by a computer. The machines put down many thin layers of material -- such as plastic, metal or concrete -- on top of each other. Objects are created through this process, from the bottom up. In recent years, 3D printers have mostly been used to create small, specialized items. This includes parts for automobiles, airplanes and medical devices. Many consumer products can also be 3D printed as well, from clothes to foods. Now, an increasing number of startup companies are using 3D printing to build entire homes. Since the technology is still developing, not many have yet been built. However, the top companies plan to greatly increase production in coming years. The startup company Icon, based in Austin, Texas, made news in 2018 by completing the first permitted 3D printed home in the U.S. At the time, it said the home had been built in just a day.