Bottom Layers Flared Out (Elephant's Foot)

Likely causes, most common first

1. Nozzle too close on the first layerMost common
   Polymaker explains that with too little gap, material builds up and is pushed out sideways, so the bottom is wider than the part. Prusa describes the same thing: the first layer is squished against the bed and ends up a bit wider than it should be.
2. Bed temperature too high for the materialCommon
   Polymaker explains that a bed above the material's glass transition temperature keeps the bottom layers soft enough to deform under the layers printed on top. OrcaSlicer also lists the weight of the material above and thermal expansion.
3. Compensation off or set wrongCommon
   Slicers can shrink the first layer to cancel the squish. Prusa says its official profiles have it on by default; a custom or imported profile may not.
4. First layer expansion set positiveOccasional
   Polymaker notes Cura's initial layer horizontal expansion widens the first layer, which helps adhesion but worsens elephant's foot.
5. Bed not levelOccasional
   OrcaSlicer lists inaccurate bed height or leveling. If the flare is worse on one side of the plate, the nozzle is closer there.

Fix it, one change at a time

1. Set the first layer height properly. Use your printer's Z offset, live adjust or first-layer calibration until the lines are flat and touching but not smeared. Re-run leveling or the bed mesh if one side is worse. See Z Offset.
2. Lower the bed temperature within the filament maker's range. If the height is right and the bed is already in range, Polymaker suggests trying a little lower still. Watch that adhesion holds.
3. Turn on elephant foot compensation. In PrusaSlicer it is under Print settings, Advanced (Advanced or Expert mode); Prusa says values around 0.2 mm usually work for the default 0.4 mm nozzle Starting point. OrcaSlicer has the same setting plus a number of layers over which the shrink fades out. Change it in small steps and test.
4. In Cura, Polymaker suggests a negative initial layer horizontal expansion for the same effect.
5. Use a raft if the other fixes are not enough. Polymaker uses one as its fallback. Note that OrcaSlicer only applies elephant foot compensation when the part sits directly on the plate, not on a raft.

Confirm it is fixed

Print a small calibration cube or the real part and measure across the bottom layer and across a wall higher up with calipers. They should match within your printer's normal tolerance, and the bottom edge should be straight when you run a fingernail up it. Check that the first layer still bonds well: if the brim no longer joins the part, Prusa says the compensation is probably set too high.

Why it happens

The first layer is deliberately pressed onto the plate harder than any other layer, because that squish is what makes it stick. Squeezed plastic has to go somewhere, and the only way out is sideways, so the outer line of the first layer ends up slightly wider than the model. A nozzle set a little too close makes the squish, and the flare, larger.

Heat adds to it. The bed keeps the bottom layers warm for the whole print, and if it is warm enough to soften them, the weight of everything above slowly pushes them outward. That is why the flare can extend over several layers rather than only the first; Polymaker notes it usually corrects itself after a few.

Slicer compensation works by drawing the first layer slightly smaller than the model, so the squish brings it back to the right size. OrcaSlicer's version shrinks the first layer by the full amount you set and reduces it evenly over the next few layers:

The preview will show the part slightly smaller at the base, and a brim may look detached. Prusa explains that the squish fills that gap on the real print. Compensation hides a nozzle-height problem rather than fixing it, so set the height first. For checking sizes after the fix, see Dimensional Accuracy.