One of the immediate applications of carbon nanotubes (CNT) is as an additive to polymers to create electrically conducting plastics–a relatively low CNT concentration can dramatically change the polymer’s electrical conductivity by orders of magnitude, from an insulator to a conductor. New measurements have uncovered an intriguing wrinkle. For a given CNT concentration, the electrical properties of the composite can be tuned from being a conductor to a non-conductor simply by changing processing conditions — basically how fast the polymer flows.