Much modern fiber isn't pulled through conduit — it's blown: compressed air floats the cable while a tractor feeds it, gliding glass through duct at a walking pace for thousands of feet per setup. Jetting is how empty conduit becomes lit network without a winch line or the friction that snaps cables.
How jetting works
A blowing machine clamps onto the duct, feeds the cable with drive belts, and injects high-volume compressed air around it. The air doesn't push the cable like a piston — it drags along the cable's surface and effectively floats it off the duct wall, collapsing friction to almost nothing. Result: installs of 3,000–6,000+ feet per setup in well-placed duct, at speeds a pull rope could never survive, with near-zero tension on the glass.
Microducts: blowing's natural habitat
Microduct systems — bundles of small tubes, each awaiting its own micro-cable — only work because of jetting: you can't pull a rope through a 10 mm tube, but you can blow a cable through half a mile of it. The model changes network economics: place the tube bundle once, then blow cables into individual tubes years apart as demand arrives — capacity on demand without ever re-opening the ground.
Blowing vs. pulling, honestly
Pulling still wins for short runs, large heavy cables, and duct with unknown condition. Blowing wins on distance, cable safety (tension is the enemy of glass), and labor per foot — when the duct is continuous, clean, and properly bent. The prerequisite is construction discipline: duct placed to spec, proofed, and lubricated. Bad duct turns a blowing day into a pulling week.