Flexible filament can be tricky to print. Slicer software settings and your 3D printer hardware both come into play when trying to get a successful print.
Slicer software settings
Mainly, print speed and retraction are the slicer software settings you need to get right. Firstly, you will want to print really slow and also make sure to turn off retraction. Constant retracting and extruding can cause under-extrusion.
3D printer hardware
The build surface and extruder type of your 3D printer are also important. When printing on a cold print bed make sure to use some sort of adhesive layer. Although, when your printer has a heated bed with a glass surface there’s a fair chance you don’t need an extra adhesive layer.
Bowden versus Direct Extruder
Back in the day, it was a general rule that it’s easier to print flexible filament with a 3D printer that has a direct extruder instead of a bowden extruder. However, times have changed and extruders have improved a lot, so nowadays you have a good chance even your bowden extruder is able to print flexible filament.
Direct extruders are placed on the moving parts of the 3D printer. The (heavier) stepper motor of the direct extruder can slow down the print speed and can decrease the print quality. Bowden printers can achieve higher print speeds and higher detail.
Aside from the choice of bowden versus direct extruder, the next most important element which decides if your printer is up to the task of printing flexible filament is the way it constrains the filament path. A fully constrained path from the idler/gear pinch point to the hot end means there is nowhere for the filament to want to come out of or bind in.
A good example of an extruder with a fully constrained filament path is the Bondtech QR. It’s available for 1.75mm and 3mm filaments and can be configured either as a direct or bowden setup.