A nanometer is one-billionth of a meter. That's impossibly small. A single sheet of paper is 100,000 nanometers. Your fingernail grows approximately 1 nanometer every second. Even a strand of your DNA is 2.5 nanometers wide [source: NANO.gov]. To construct materials at the "nano" scale would seem impossible, but using cutting-edge techniques like electron-beam lithography, scientists and engineers have successfully created tubes of carbon with walls that are only 1 nanometer thick.
When a larger particle is divided into increasingly smaller parts, the proportion of its surface area to its mass increases. These carbon nanotubes have the highest strength-to-weight ratio of any material on Earth and can be stretched a million times longer than their thickness [source: NBS]. Carbon nanotubes are so light and strong that they can be embedded into other building materials like metals, concrete, wood and glass to add density and tensile strength. Engineers are even experimenting with nanoscale sensors that can monitor stresses inside building materials and identify potential fractures or cracks before they occur [source: NanoandMe.org].