How to reduce filament waste in 3D printing
Most wasted filament is multicolor purge and supports. On multicolor prints, the biggest saving is fewer filament swaps, not smaller purges. Unlayered Slicer reduces swaps by printing in planes.
Why multicolor printing wastes filament
A single-nozzle system like a Bambu Lab AMS purges the old color on every change. A planar slicer changes color whenever a layer holds more than one, so an accent running the full height of a tall model means a purge every layer, and the purge can outweigh the part.
Reduce the number of swaps
A swap that never happens wastes nothing. Unlayered Slicer prints in planes, reducing how many swaps have to happen, which cuts both purge and prime tower. In the design, keep accent colors to few layers and fill the plate so each swap serves more parts.
Reduce purge and prime tower waste per swap
Dark to light needs far more purge than light to dark, so tune flush volumes per color pair. Flush into infill, supports or a sacrificial object instead of the chute, and shrink the prime tower to the smallest stable width.
Print fewer supports
Orient overhangs upward and use tree supports when unavoidable; they use less material than grid supports. Flat overhangs can skip supports entirely with wave overhangs.
Other ways to save filament
Calibrate flow to stop over-extruding, use two or three walls and low infill on non-structural parts, and dry your filament: a failed print wastes more than any purge.