Curaprox interdental brushes are the world's best. They won't bend or break and you will get 12 - 16 days use from each brush. They definitely won't rust.
This is the CPS09 brush in a pack of 50. The most economical way to order. The CPS 09 brush will fit into a space as small as 0.9mm and will clean a space as large as 4mm.