They work by combining a waxy substance with a yarn made of carbon nanotubes. The wax expands in response to heat (or a voltage), and the yarn volume increases while its length contracts. This happens because it's twisting, as a news release from UT Dallas explains. As the wax melts or solidifies, it twists and untwists, generating motion. The yarn can be looped, sewn, braided or whatever else you do with yarn, so it could be easy to use it in new types of textiles. You could design blankets that get thinner when it's warm, maybe, or tapestries that tell you which chemicals are in the air.