You can adjust the hardness of the damper by adjusting the density of the filling. I recommend staying at 100% for damper Y-axis because the length of the belt imposes a high tension, which may cause the sagging of the damper. I recommend printing at a high enough temperature to optimize adhesion between the two filaments. I printed these parts to 248 °. Warning : For an optimal result you must think about indexing the filament flux on the semi-flex and not on the PET! In order to guarantee a homogeneous, solid silent block and the good adhesion of the semi-flex on the PET, you must deactivate the cooling when you go from PET to semi-flex. You will restart cooling for the final part of PET printing. Filaments used: -Innofil PET EPR (Red) -Recreus 95A FILAFLEX Medium Flex (Blue) Remember to include two M600s in your gcode if you do not change your fil in manual mode. Ex: M600 E-10 L-50 X40 Y40 Z100 The syntax of this command is detailed here:http://marlinfw.org/docs/gcode/M600.html