ELEPHANT FOOT (BULGING FIRST LAYERS)

Elephant foot is a three-variable interaction between Z-offset, bed temperature and first-layer flow. Each variable controls a different physical step of the same problem - too much plastic, with nowhere vertical to go, kept fluid long enough to squash sideways under accumulating weight. Start with the geometry. A first layer deposited at the correct gap looks like a flattened tube about 120% as wide as it is tall - the nozzle squashes the molten extrusion against the bed and forces it sideways into a controlled spread. That 120% is intentional and is what gives the layer its mechanical bond to the bed surface. At too small a gap there is no vertical space at all, so the nozzle forces every bit of plastic sideways because it has nowhere else to go, and the spread goes well beyond the model footprint. At too large a gap the line stays round and bonds weakly. Z-offset sets that initial compression. Bed temperature controls how long the deposited plastic stays plastic. PLA at 60C, PETG at 80C, ABS at 110C - the bed is hot enough that the polymer chains in the bottom layers stay above their glass transition for several minutes. As long as the base is soft, any pressure deposited on top of it will move it. First-layer flow controls the total volume of plastic in the layer. More volume means more material to spread when the nozzle squashes it, and more material to redistribute under load. What makes it worse is layer weight accumulation. The print accumulates mass over the first 3-5 layers, and the moving toolhead adds dynamic forces beyond just static weight. If the bed stays at full first-layer temperature instead of dropping 5C after layer 1, the base layers remain pliable and continue spreading under that growing load. This is exactly why large flat-bottomed prints get worse elephant foot than small ones - more mass above the still-soft base, longer time spent at bed temperature before the print finishes, and more dynamic toolhead forces redistributing soft plastic. Slicer compensation works by predicting the spread and pre-shrinking the first-layer outline by the predicted amount. If your setup spreads first layers outward by 0.15 mm, telling the slicer to inset the first layer by 0.15 mm produces a final bottom that matches the model dimensions. The compensation value is per-printer and per-filament, but once you find it, it holds across all prints with that combination.