Printing flexible material can pose unique challenges. Most of us are used to PLA or ABS, which is somewhat rigid before it melts. So, extrusion is pretty straightforward. Flexible filament, however, can be a lot like pushing a rope. If you are printing flexible filament on your Printrbot, you will probably want to upgrade to the Gear Head Extruder v2, if you haven't done so already.
Slowing your print speed (20mm/sec) and increasing your temperature (222C) will also improve your results. Download the configuration profile (.ini) below and try the "Printrbot blessed" flexible settings.
* For instructions on loading a profile along with additional material configurations, click here.