How do you cool extruded plastic filament without a water bath?

You can cool extruded plastic filament without a water bath by carrying the hot strand on a belt under jets of compressed air, which keeps moisture-sensitive polymers dry at the cost of a slower, longer cooling run.

The short answer: forced air on a moving belt

To cool extruded plastic filament without a water bath, you lay the hot strand on a conveyor belt and blow air over it as it travels, so heat leaves by forced convection and the plastic never touches water. Commercial strand-cooling belts for pelletizing lines work this way, and a 2026 open-source design published in the journal HardwareX, the Air-Cooling Conveyor, shows the same idea can be built for a lab bench out of 3D-printed parts.

Air removes heat more slowly than water, so the trade is a longer cooling path or a slower line in exchange for a dry, gently handled strand.

Why filament and strands are normally cooled in water

Plastic leaving an extruder is soft and has to be cooled before it can be wound on a spool or chopped into pellets. In typical 3D printing filament production, the strand is pulled rather than pushed out of the die, so the pulling speed sets its diameter, and a laser gauge often checks that diameter on the fly. The strand then runs through a warm water tank that helps it set round and a cold water tank that brings it down to room temperature.

Water is popular because it soaks up heat fast and the strand solidifies quickly in a short space. That is why many small filament makers also offer water baths alongside air-cooled paths, mainly to stabilize shape for large diameters and high-temperature materials.

What goes wrong when the plastic hates water

Many thermoplastics are hygroscopic, meaning they pull moisture from their surroundings. Nylon and PVA are the familiar examples in 3D printing, and damp plastic causes dimensional flaws when it is extruded. Pellets are usually dried before extrusion for exactly this reason, so dunking the fresh strand in water can undo that work.

Equipment makers point to a few specific problems with water cooling: moisture degrades PLA and harms several engineering plastics, some high-temperature and bio-based or water-soluble medical polymers cannot be water-cooled conventionally at all, and a water bath needs process-water handling plus drying afterward. One supplier of engineering filaments built a multi-jet air extruder specifically to keep its strands away from water, and claims tighter ovality and diameter tolerances as a result, though that is a company claim rather than an independent test.

How an air-cooling conveyor is built

Industrial strand-cooling belts drop the strands straight onto a moving belt and cool them with high-capacity air nozzles on the way to the pelletizer. Their makers list no manual strand threading, low mechanical stress, no process water treatment and easy cleaning as the benefits. One variant uses a solid stainless steel belt with water flowing underneath and fans above, so water carries heat away without ever touching the polymer.

The open-source Air-Cooling Conveyor follows the all-air approach at lab scale. A PTFE-coated belt, chosen so the polymer does not stick, carries the strand under arches that emit compressed air. An Arduino with a potentiometer sets the belt speed through a small 12 V DC motor, and the frame is printed in PLA from FreeCAD models. In the reported tests, air at 2 bar and a belt speed of about 1.8 cm/s gave roughly 45 seconds of cooling over the validated length of about 82 cm.

How well it works and where it falls short

Across nine infrared-camera trials with PLA, polyamide and polypropylene, the conveyor cut strand temperature by 48 to 57 percent, about 51 percent on average. Polyamide entering at around 195 to 208 C dropped by about 107 C on average, and the cooled strands were cut cleanly by a pelletizer without sticking or deformation. The parts cost about 230 euros, against roughly 1,195 US dollars for the nearest commercial kit.

The limits are real. Printed PLA parts soften near 55 to 60 C, so they must stay clear of the nozzle and hot polymer, or be reprinted in a tougher plastic such as PETG, ABS, ASA or polycarbonate. Length and throughput are capped by motor torque and belt stiffness, loads were kept under 500 grams, and the air jets run at about 78 decibels. For fast production lines water still wins on raw cooling power; air belts earn their place where moisture, cleanliness or gentle handling matter more than speed.