These structures are called nanotubes. They’re made out of carbon, and there are millions of them in a coating of Vantablack. Indeed, a coating the size of a thumbnail would be made of about 1,000 million nanotubes. So it’s fair to say that the nanotubes are small, then, but it’s also important to understand just how small.
Each of the nanotubes is about 20 nanometers long. Or in other words, you’d need more than 3,000 of them bundled together to get something with the same width as a single human hair. And it’s thanks to the super high concentration of these minuscule objects that Vantablack is able to absorb so much light.