It’s hard to study something with any rigor if the subject can’t be produced uniformly and efficiently. Researchers who study double-walled carbon nanotubes find themselves in just this predicament. The problem is that current techniques for synthesizing double-walled carbon nanotubes also produce unwanted single- and multi-walled nanotubes. Researchers now offer a clever solution: They used a technique called density gradient ultracentrifugation to cleanly and easily separate the double-walled nanotubes from the undesirables.