Bridging

Bridging is when a printer extrudes filament across an open gap — for example, spanning the top of a hollow cube or connecting two pillars. The filament is stretched taut between two anchor points, and when done correctly, the result is a clean horizontal span with no drooping.

How Good Bridging Works

Successful bridging requires three things working together:

1. Tension: The extruded filament is pulled tight between two points. The nozzle moves quickly enough that the molten plastic is stretched rather than allowed to sag.
2. Cooling: The part-cooling fan must rapidly solidify the bridge as it’s laid down. Poor cooling = saggy bridges.
3. Flow control: The slicer reduces extrusion during bridging (typically to 80-95% of normal flow) to prevent excess material from weighing down the span.

Bridging Settings That Matter

Setting	Effect
Bridge flow ratio	80-95%. Less material = lighter bridge = less sag
Bridge speed	20-40mm/s. Fast enough to stretch, slow enough to cool
Fan speed during bridges	100%. Maximum cooling is essential
Bridge skin support threshold	0-10%. Determines when supports are generated instead

Testing Your Bridge Performance

The classic bridging test is a series of horizontal gaps at increasing distances. Most well-tuned printers can bridge 50-80mm with PLA without significant sagging. PETG typically bridges 30-50mm. TPU and flexible filaments cannot bridge effectively.

Common Bridging Problems

• Sagging/drooping: Too slow, too hot, or insufficient cooling. Solution: increase bridge speed, decrease nozzle temp 5-10°C during bridges, check fan.
• Rough/textured bridges: Over-extrusion during bridging. Solution: lower bridge flow ratio to 85%.
• Broken bridges: Too fast, causing the filament to snap. Solution: decrease bridge speed, increase flow slightly.