PETG Bridging and Overhangs: What to Expect

PETG owners often think their bridging settings are broken because the same model bridged beautifully in PLA. They aren't broken — PETG plays with a handicap: the cooling that makes bridges possible is exactly what PETG's layer bond can't take too much of.

The built-in handicap

PLA bridges under a 100 % fan. PETG’s stock cooling window is 30–60 % — because past it, PETG’s layer weld (its best feature) starts to suffer. The profile does grant a temporary exception over overhangs and bridges: 90 % overhang fan. That asymmetry — modest cooling everywhere, strong cooling only where geometry demands it — is the entire PETG bridging strategy, and it still lands short of PLA. Expect competent 30 mm bridges and clean overhangs to roughly 45°, not PLA’s 55–60°.

Getting the most out of it

1. Verify the overhang fan boost is active. If a strength-focused profile flattened all cooling to 30 %, bridges lost their exception. Restore overhang fan to 90 % — the few seconds of extra fan on a bridge does far less bond damage than people fear, and the bridge actually forms.

Filament settings → Cooling → Overhang fan speed

2. Slow the bridge right down. 20 mm/s bridge speed. PETG’s melt is heavier and stays workable longer than PLA’s; it needs the extra dwell time under the fan.

Process → Speed → Bridge

3. Print bridge-heavy parts at the cool end. Stock nozzle is 250 °C; toward 230 °C the melt sets noticeably faster mid-span. Accept the slightly matte finish on those prints.

4. Dry the spool. A wet PETG bridge doesn’t sag — it drips. Steam pockets burst mid-span and leave hanging loops. 8 h at 65 °C; with PETG, always rule out water first.

Design around it

Calibrate expectations, then the printer

Print a small bridging test in PETG after the fixes above: a clean 30 mm span with slight underside texture is PETG-good. Chasing PLA-glass undersides in PETG leads people to max the fan, and two weeks later they are diagnosing cracked layers instead (that guide is here). If a model truly lives or dies on bridging quality, print it in PLA — that is engineering judgment, not defeat. General bridging mechanics: the main bridging guide; the everyday PETG numbers: the PETG settings guide.

Frequently asked questions

Why does PETG bridge worse than PLA?

PLA bridges under a 100 % fan, while PETG’s stock cooling window is only 30–60 % — past that, its layer weld, PETG’s best feature, starts to suffer. The profile grants one exception: a 90 % overhang fan over bridges and overhangs. Even well tuned, expect competent 30 mm bridges and clean overhangs to roughly 45°, not the 55–60° PLA manages.

What settings improve PETG bridging?

Four levers: verify the overhang fan boost is active at 90 % (strength-focused profiles sometimes flatten all cooling to 30 %); slow bridge speed to 20 mm/s so the heavier PETG melt gets dwell time under the fan; print bridge-heavy parts toward 230 °C instead of the stock 250 °C; and dry the spool 8 hours at 65 °C — wet PETG doesn’t sag mid-span, it drips.

Should I use supports for PETG overhangs?

Yes for overhangs steeper than about 45° and for long spans — but set a generous support top gap of 0.2–0.25 mm, because PETG welds to its own supports far more eagerly than PLA. Better still, design around it: replace 90° ceilings with 45° chamfers, reorient the part so its worst bridge becomes a flat bottom, or add a snap-off 0.8 mm sacrificial rib under a long span.

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