Drooping overhangs and sagging bridges: cooling, speed, and slicer checks

This guide is for anyone seeing droopy undersides, curled edges on steep angles, or bridges with strands hanging into the gap. It explains what each symptom points to, how the advice differs between PLA, PETG, and ABS or ASA, and why an enclosure can work against cooling.

What do drooping overhangs and sagging bridges look like?

• Drooping or rough overhangs. The underside of an angled surface looks ragged or stepped, and gets worse as the angle gets steeper.
• Curling edges. The edges of an overhang curl upward as the print goes on. Polymaker notes that this can look like warping, but the individual layers curl up instead of the part lifting off the bed. Simplify3D says curling "later on in your print" typically points to overheating.
• Sagging bridges. Strands across a gap hang down, break, or look loose. Prusa calls sagging or drooping "the typical problem of bridging layers."
• Melted small features. Tips of cones and small towers lose their shape. Simplify3D treats this as overheating: the plastic "was not able to cool quickly enough to retain its shape."

Note where the problem shows up: on every overhang, only on one side of the part, or only in one material. Polymaker suggests turning overhangs to face the cooling fan, so droop on one side only is worth noting before you change settings. One print won't tell you for certain, so use the symptom to decide what to check first.

Step 1: Start from a known-good profile and check the fan

Use your printer maker's slicer profile for your exact printer, nozzle, and material, and print a small overhang or bridging test as a baseline. Then do the cheapest hardware check: watch the part cooling fan during a print. Polymaker's advice is to "confirm fan functionality before extended prints." Polymaker also advises aiming the fan duct at the extruded plastic, not the nozzle.

Prusa's cooling documentation also notes that most printers come with a dedicated print fan, and that "by blasting ambient air at the extruded filament, the cooling can be dramatically improved." It adds a warning that matters later: with some materials, that same airflow "could make things actually worse and cause warping or layer separation."

Step 2: Set part cooling for the material

Cooling is the first lever for overhangs and bridges, but how much depends on the plastic.

PLA

Polymaker's cooling guide says PLA needs active cooling for clean overhangs and bridges, typically 100% fan "to prevent layer curling and sagging," with large, thick PLA parts tolerating 70–80%. Its curling guide says PLA printing typically needs the fan at 100% "following the completion of the first layer," and that printing PLA without active cooling "consistently results in surface imperfections and top-layer curling." If PLA overhangs droop, check the fan speed first. Our PLA printing problems guide covers other PLA-specific fixes.

PETG

PETG is harder. Prusa's PETG guide lists "poor bridging and overhangs" among its drawbacks and says its "bridging- and overhang-behavior is usually worse" than PLA's. Prusa says cooling PETG helps keep the model detailed, and recommends printing the first few layers with the fan off, then running it "at half its power." It also says turning the fan off makes the part tougher, so you're trading strength for detail. Polymaker gives 50–80% as an example PETG fan range. These numbers vary by brand and blend. Our PETG printing problems guide covers other PETG-specific fixes.

ABS and ASA

These need much less cooling, and too much causes its own failures. Prusa's cooling article says "Keep fan always on" is typically enabled for most materials "with the exception of ABS, ASA, PC, and some flexibles." Polymaker recommends minimal or no active cooling for medium and large ABS, ASA, and PC parts, and 20–50% only for small features such as pins and thin walls. Expect steep overhangs and long bridges in these materials to need supports or a different orientation, because you can't cool them as hard as PLA. See ABS vs ASA for more on these materials.

Step 3: Use your slicer's overhang and bridge cooling

Most slicers can raise the fan only where it's needed, which avoids over-cooling the rest of the part:

• PrusaSlicer. "Bridges fan speed" overrides the fan speed "when printing bridges and overhangs," and Prusa says you'll typically set it higher than for normal printing. "Dynamic fan speeds" varies the fan by how much a line overhangs the layer below.
• OrcaSlicer. "Force cooling for overhangs and bridges" enables a separate fan speed for overhangs and bridges. An "overhang cooling activation threshold" sets how much of a line must be unsupported before it kicks in.
• Cura. "Enable Bridge Settings" detects bridges and changes speed, flow, and fan while they print. Its "Bridge Fan Speed" defaults to 100% when enabled. Cura's description of print cooling says the fans "improve print quality on layers with short layer times and bridging / overhangs."
• Simplify3D. The "Bridging fan speed override" sits on the Cooling tab. Simplify3D says you typically want it at "a large value."

For ABS and ASA, this per-feature approach is how you get some overhang cooling without cooling the whole part.

Step 4: Bring the nozzle temperature down within range

Hotter plastic stays fluid longer. Simplify3D suggests lowering the print temperature by 5–10 degrees if overheating persists with the fan running, and warns not to go so low that the plastic won't extrude. Polymaker suggests 5–15 °C lower for bridges and 5–10 °C lower for overhangs. Stay inside the range printed on your spool or in the filament's data sheet. A temperature tower, as described in our stringing guide, lets you compare several temperatures in one print.

Step 5: Slow down where it matters

Speed controls how long each line has to set before the next one lands on it.

• Overhang speeds. OrcaSlicer's "Slow down for overhang" uses different speeds for different overhang degrees, and "Slow down for curled perimeters" adds extra slowdown where perimeters may curl, such as the front of a Benchy hull. Cura's "Overhanging Wall Speeds" prints walls past the overhang angle at a percentage of normal speed.
• Bridge speed. Prusa recommends "lower speed for printing bridges." Polymaker gives 15–30 mm/s as typical. Simplify3D is more cautious: "some printers will perform better with slow bridging, while others get better results by moving quickly." Test on your own machine.
• Minimum layer time. Small parts can finish a layer before the last one has set. Simplify3D recommends slowing small layers down so they have time to cool. Cura's "Minimum Layer Time" and the PrusaSlicer and OrcaSlicer slowdown thresholds do this automatically. Simplify3D also suggests printing two copies at once so each one gets more time to cool.

Step 6: Tune bridge flow and bridge settings

Sources disagree here, which is a good reason to test rather than copy a number:

• Prusa says the first bridging layer "should be done with a lower flow," so the strand is pulled along behind the nozzle and "drops less." In PrusaSlicer this is the bridge flow ratio.
• OrcaSlicer says reducing the flow ratio can help when external bridges sag, while increasing it for internal bridges improves strength. It also offers thick bridges, which it says improve strength and reliability for longer spans but may look rougher, and an extra bridge layer option.
• Polymaker suggests slight under-extrusion on bridges, around 90–95% flow.
• Simplify3D takes the opposite view and says you typically want its bridging extrusion multiplier at 100% or more, because lower values "may have trouble properly sealing the bottom of these surfaces."

Prusa suggests putting several copies of a bridging test model in the slicer, each with a different flow, and printing them together. That finds a working value in one print.

Also check that the slicer is detecting the bridge at all. Simplify3D's guide shows bridging regions in a separate color in the preview, and notes that small areas below a threshold are ignored. It also says bridge lines should run across the span between the two supports; Simplify3D sets that direction automatically once the region is detected.

Step 7: Consider layer height, carefully

Layer height affects overhangs, but not in one simple direction. Polymaker's overhang article says a thinner layer leaves less unsupported area at the same angle, but is also "less rigid," and that "it will always be a balance between rigidity and amount of unsupported area." It says the best overhangs generally come from "a high layer height (more rigidity), low printing speed ... and high extrusion rate." Polymaker's cooling guide, on the other hand, suggests 0.2 mm or thinner to reduce overhang angles. Treat layer height as a later test, and change it by itself.

Step 8: Change the geometry: orientation, supports, and design

When settings run out, change what the printer has to print.

• Reorient the part. Prusa calls changing the orientation "the best solution," and says the rule of thumb is to "avoid bridges and supports completely" where possible. Polymaker also suggests turning the model so overhangs face the cooling fan.
• Add supports where needed. Cura's "Support Overhang Angle" defaults to 50°, meaning that when support generation is turned on, overhangs steeper than that get supports. For a very long bridge, Prusa suggests a support enforcer halfway across. Simplify3D recommends supports when tuning can't get a bridge right.
• Let the slicer reshape the overhang. OrcaSlicer's "Make overhang printable" changes the geometry so steep overhangs become printable without supports, and says a maximum angle "between 45° and 60° works well for most printers and models."
• Design for printing. Prusa's design guide says a fillet facing the bed creates "a very steep overhang," and recommends a chamfer instead. Splitting a part into pieces that each print in a better orientation can reduce supports too. Polymaker suggests shortening spans with arches, ribs, or small support tabs.

Prusa notes that its printers with the Nextruder and 360° cooling (MK4S, CORE One and CORE One+, CORE One L) can print overhangs up to 75° without supports. That figure is for those printers, not a general target.

When does an enclosure work against cooling?

An enclosure keeps the air around the print warm. That helps ABS and ASA, but it's the opposite of what PLA overhangs need.

• PLA and PETG in enclosed printers. Bambu Lab recommends opening the front door and/or removing the top glass cover when printing materials that soften below 60 °C (such as PLA, PVA, and TPU) with the bed above 45 °C, and PETG with the bed above 60 °C. The reason it gives is that excess chamber heat can soften filament inside the extruder, which "can cause abnormal extrusion or clogging." It adds that this matters more when the room is warm.
• ABS and ASA. Prusa lists an enclosure as required for ABS and necessary for large ASA parts, to keep the ambient temperature higher. Polymaker says an enclosure maintains the ambient temperature, "reducing reliance on active cooling." So with these materials, expect to lean on supports and orientation rather than fan speed.
• Heat-sensitive printer parts. Prusa warns that printing ABS inside an enclosure can deform the fan shroud and other plastic parts, and that printing a lot of ASA in an unventilated enclosure can deform the fan shroud and extruder parts over time.

An enclosure isn't a ventilation system. Heated plastics release particles and vapors, so plan ventilation separately. Our enclosure planning guide covers heat, electronics, and air, and the Enclosures: what to check before you buy ↗ lists related reading.

Other causes worth ruling out

• Wet filament. Polymaker says poor bridging can come from wet filament, which causes "bubbling and inconsistent extrusion." See our dryer vs dry box guide, and our filament dryers shortlist if you decide you need a dryer.
• A dirty nozzle tip. Polymaker notes that residue on the nozzle can drag the strand during bridging.
• The wrong material for the job. If a part needs long unsupported spans, PLA is usually easier than PETG. Our PLA vs PETG guide compares them by what the part has to do.

A sensible test order

1. Reset to your printer maker's profile and print a small overhang and bridge test.
2. Watch the part fan and confirm it runs and points at the print.
3. Set fan speed for the material, using overhang and bridge fan overrides.
4. Run a temperature tower within the spool's range.
5. Lower overhang and bridge speeds, and check minimum layer time.
6. Test bridge flow with several copies in one print.
7. Reorient, add supports, or adjust the design.

Change one thing per print and note the result.

When should you hold off on buying parts?

Hold off on an upgraded fan duct, a new hotend, or a different printer if:

• You haven't confirmed the existing fan runs and isn't blocked.
• You're on a custom or borrowed profile rather than the printer maker's.
• You haven't tried the slicer's overhang and bridge fan settings.
• The part could be reoriented or supported instead.
• You're printing PLA in a closed enclosure with the door shut and a warm bed. Bambu Lab advises opening the door or lid for PLA once the bed is above 45 °C.

If a fan is genuinely failing, use the replacement part your printer maker specifies for your exact model. Third-party ducts and fans vary by printer and revision, so check fit and the maker's documentation first.