The United States has the largest number of prison inmates in the world—more than two million people. And because the laws for inmates are so strict, the only way to listen to music is via the antiquated medium of cassette tape. This is because both CDs and vinyl records can be easily fashioned into weapons. There are companies that produce a special kind of screwless, sonically welded cassette tape made out of clear plastic (seen in the picture above).
In 2013 Chris Barrett, who was running SendAPackage.com to make it easy to ship packages to inmates, got a deal with Universal to produce any album available on tape if he purchased 250 copies of it. Major indies like Sub Pop also plan to release every album on cassette in the coming year.