What is the technology behind8 Professor Jacobson’s book? Two important inventions9 will make this new kind of book possible: electronic ink and radio paper. Electronic ink — or “e-ink” — is a liquid that can be printed on paper, metal, or anything else. E-ink looks and feels like printed words on paper. Unlike regular ink, however, words in e-ink are not permanent. They can be changed by pushing a button. When you push the button, all of the words on the page go away and new words appear.