The interiors are meant to stay concealed yet your print’s exteriors is showing the outline of the internal structure. This is called ghosting in the 3D printing community. It is not all bad though as ghosting helps your print to bond better. It is brought on when the infill overlaps with the perimeter line as it is being laid down. It can also be caused by setting the wrong wall thickness in comparison to the nozzle size that is equipped in your 3D printer.
You can fix it by fixing the settings in your slicing software.
- Adjust the shell thickness: The shell thickness should be set in a value divisible by the nozzle size. You could also try increasing the shell thickness to cover the overlap.
- Recalibrate your printer: If you find that the ghosting only happens more on one side than the other, it could be that you need to recalibrate your 3D printer.
- Print the infill last: Slicing software programs allow infill to be activated after perimeters.
- Prioritize the shells: You can opt to print Outside-in instead of the usual Inside-out to ensure a good surface finish. However, choosing the former can be detrimental to the strength of the print and is only advised if strength isn’t important for your model.