This is on add on for the duplo compatible marble run. It allows to use plastic filament as track! I had on old spool of flexible that I never to manage to print with...find it a second life!
I just added holes in the normal pieces to fit the filament. I also added a ramp 2x4 pieces with a smaller slope (I find the original going to fast!).
Printing 0.2mm, no support on Prusa I3, worked like a charm.