A new plastic conducts heat only in one direction

Polymers are generally put to work as insulators, but a team of researchers at MIT has devised a way to turn polyethylene -- the most commonly used polymer -- into a conductor that transfers heat better than many pure metals. But the conversion of insulator to conductor is only half of the breakthrough; by coaxing all the polymer molecules into precise alignment, the researchers have created a polyethylene that conducts heat in only one direction. The plastic material remains an electrical insulator...

With a thermal conductivity 300 times greater than conventional polyethylene, the polymer is actually more conductive than about half of all pure metals, meaning it could potentially replace metal conductors in several common devices.

Addendum: See Darren's note in the Comments section. The use of the term "one direction" in this article appears to be in the context of "one dimension" (or one axis, if you will) - i.e. a plastic that might transmit heat longitudinally but not laterally or vertically - but the heat could still go back and forth along that axis depending on the direction of the gradient.