Why is the first layer height different from the rest of the print?

The first layer is the foundation. A taller, wider first layer (typically 0.2 to 0.3mm height and 100 to 150% nozzle width regardless of the model's layer height) increases the contact area and squish against the bed, dramatically improving adhesion. Thin first layers grip poorly and lift.

What does 100 to 150% line width mean?

Line width is expressed relative to nozzle diameter. On a 0.4mm nozzle, 100% is a 0.4mm wide line and 150% is 0.6mm. A wider first-layer line lays down more plastic per pass, fills the surface texture better, and resists peeling. The slicer extrudes more filament to fill that width.

Can the first layer be too thick?

Yes. A first layer taller than about 75% of the nozzle diameter is hard to push through and can blob or under-adhere. The optimizer caps the first-layer height at roughly 75% of the nozzle to stay printable, which is why a 0.4mm nozzle tops out near 0.3mm.

Does the bed surface change the recommendation?

Yes. Smooth surfaces (glass, smooth PEI) grip on squish, so a slightly higher squish and standard width work well. Textured PEI has deep valleys, so a wider line helps fill them. Tape and glue stick are forgiving and use moderate settings.

How does this help with elephant's foot?

Elephant's foot is over-squish on the first layer. If you see bulging bottom edges, raise the first-layer height slightly or reduce flow on the initial layer. This optimizer aims for firm but not excessive squish to keep edges crisp.

First Layer Line Width Optimizer

The first layer makes or breaks a print. This optimizer recommends a first-layer height and line width tuned to your nozzle, layer height, and bed surface to maximise adhesion without over-squishing into elephant’s foot.

How it works

Two settings drive first-layer adhesion: height and width.

First-layer height is set independently of the model’s layer height. A thicker first layer squishes more plastic against the bed for grip, but a layer taller than the nozzle can extrude can blob. The rule of thumb is 0.2 to 0.3mm, capped at about 75% of the nozzle diameter. The optimizer picks a value in that band, never below your model’s layer height and never above the 75%-of-nozzle ceiling.

First-layer line width is expressed as a percentage of nozzle diameter. A wider line (100 to 150% of the nozzle) lays down more plastic per pass and fills surface texture, which resists peeling. Textured surfaces get the wider end; smooth surfaces the lower end.

Worked example

Nozzle: 0.4mm, model layer height: 0.2mm, surface: textured PEI
First-layer height: 0.28mm (in the 0.2-0.3 band, under the 0.30mm 75%-of-nozzle cap)
First-layer width: 140% = 0.4 x 1.40 = 0.56mm (wider to fill the texture)

On smooth PEI the same nozzle would suggest around 120% width (0.48mm) with similar height.

Tips and notes

Always tram (level) the bed and set a correct Z-offset first — no width setting fixes a bad first layer.
If bottom edges bulge (elephant’s foot), nudge first-layer height up or drop initial-layer flow a few percent.
Slow the first layer (around 20 mm/s) so the wider, taller line has time to bond.
Clean the bed; oils from fingerprints defeat any adhesion setting.

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