Filaflex is really nice. It isn't super consistent in diameter, but it is a nice soft rubber.

We have printed more with NinjaFlex, which is similar. It is super strong. Ninjaflex isn't as soft as Filaflex. It is more like a car tire rubber than a soft squishy rubber. We have a couple videos here:

https://www.youtube.com/watch?v=1abQwCeT6gg

https://www.youtube.com/watch?v=ZnJZTwrQcQI

-Jeff