The cord I use is twisted nylon (usually C-lon or Superlon brand) and is available in four different sizes. I favor the middle of the road size, which is in diameter. It will fit through an seed bead and an bead will accommodate two cords.
Macrame is so hot right now and we’re totally addicted. There’s some fantastic macrame kits out there, but to get started why not grab any yarn, string, thick thread or twine you have lying around and try some of theseREAD