Stephen Heston, inventor of NinjaFlex

As you can see by these Fenner Labs Engineer Talk videos Stephen Heston knows a lot about flexible filament and extruders. He is now part of Diabase Engineering, a group of Mechanical Engineers with many years of history and interest in the 3D printing community. Their soon to be released Flexion Extruder addresses a huge need in the 3d industry.

Most stock extruders are not designed to print flexible filament and users suffer. The Flexion Extruder is a highly-engineered, precision-machined flexible filament extruder upgrade. A fully-supported path between drive and hotend allows you to print filament down to 60 ShoreA (even more flexible than Ninjaflex). It offers high speed printing and a self-cleaning drive.  Look for the product launch in early June.