Ethically Sourced Leather.
Comes with everything you need.
Spacers to go between your keys, key rings, extension rods in case you have a ton of keys, even a second strap for the rare case when you wear one out!
I would recommend that once you have decided which keys you want to leave on this key organizer, you place a single drop of blue thread-lock (available at any hardware store) in the female end of the mechanism to ensure that it never loosens. I carried mine for a year without doing this, but they occasionally do loosen from usage, heating, and cooling. This applies to all key organizers of this nature.