Gold medals have 28 small steel pellets, silver medals have 20, and bronze have 18. The idea is to provide a sensory experience for visually impaired athletes.
The medals also feature "Rio 2016 Paralympic Games" written in Braille.
This video from the Brazil 2016 channel shows how the national mint made the Olympic and Paralympic medals, including the process for placing the rattling pellets inside them.
It's worth mentioning that the Paralympic athletes also received a plush doll of Tom, the Paralympic Games' mascot, with hair in the color of the medal.
Below, Brazilian Verônica Hipólito clutches her silver-haired Tom doll while showing off her silver medal.