The infill percentage for the coffee parts will depend on your choice of flex filament. Your settings might need to be different, here are mine as a guideline:
CUP printed in Das Filament white PLA on 215°C with a 50°C heated bed on the Creality CR-10. 100% infill. 0.1 mm layer height. Fan 100%.
Latte COFFEE printed upside down in Recreus3D FilaFlex Skin II on 230°C with a 40°C heated bed on the Monoprice Select Mini. 100% infill (lines) so it is stiff enough. 0.2 mm layer height. Fan 20%. Minimal to no retraction. Initial layer pattern is concentric (Cura setting) to better mimic coffee.
Black COFFEE printed upside down in Polymaker PolyFlex Black on 230°C with a 40°C heated bed on the Monoprice Select Mini. 30% infill so it's not too stiff. 0.2 mm layer height. Fan 20%. Minimal to no retraction. Initial layer pattern is concentric (Cura setting) to better mimic coffee. I scaled it down to 99% for a better fit with this material. You might have to test this with the material you'll be using as well.
I've tried various flexible filaments on the market (definitely not all of them) and for this specific project I found the ones above to be working best, stiffness and colour availability wise. I would love to hear your experience with other filaments, as well as the ones that I've used. And of course I'd love to see your prints!
All parts were designed in Fusion360. Packaging and logo were drawn on paper, scanned, Photoshopped, screen printed, cut, folded, assembled and glued by me as well.
In case you're wondering why the Schrader coffee part has a thin hole going up higher than the actual valve does. This is to give the top part extra rigidity, so it better snaps in place and stays there. Especially needed when printing with extremely soft filament.