A Maker Is 3D Printing With Hollow Air-Filled Tubes Instead of Solid Plastic

Printing With Air

Standard fused-filament printing deposits solid lines of plastic. Layer by layer, the part fills with material. That is simple and reliable, but it is also slow and wasteful for large objects. A boat hull or a structural bracket does not need to be solid throughout to do its job.

Jan Roetz, operating under the name Roetz 4.0, decided to skip the solid fill entirely. His experimental setup uses a custom circular nozzle with a compressed air line running through the center. Molten plastic exits the nozzle in a ring, and air pressure inflates it into a hollow tube mid-flight. The result is a strand that is mostly air by volume, yet rigid enough to support weight once it cools.

The Hardware

Roetz did not buy an off-the-shelf hot end for this. He designed and built an open-source co-extrusion system called the Roetz-End, with four independent melt channels and a custom nozzle geometry. The air-injection setup is separate from the melt channels, mounted so that compressed air flows through the core of the extrusion as it leaves the nozzle.

The concept borrows from industrial blow molding, where a tube of hot plastic is inflated inside a mold to take its shape. Roetz removed the mold and let the tube free-form in air, controlled only by the print head path and the inflation pressure. It is a hybrid of 3D printing and blow extrusion that does not exist in any commercial machine today.

Why It Could Matter

If the technique ever becomes reliable, the gains are substantial. A wall built from hollow tubes could contain 80 to 90 percent air while still supporting load, thanks to the natural strength of cylindrical geometry. Material use drops sharply. Print times drop because each pass deposits a much thicker cross-section than a standard 0.4 mm nozzle line.

For large-format printing, that is the entire point. A boat hull, a architectural mock-up, or a shelter component does not need a fine surface finish. It needs volume and speed. Hollow-tube deposition could make those prints practical at scales where solid FFF is currently too slow and too expensive in material.

Where It Stands

Roetz has posted progress updates and open-source design files, but the system is not printing production-ready parts yet. After extensive testing, the team could not reliably produce a simple single-wall cylindrical vase. Variables like nozzle temperature, air pressure, extrusion speed, and cooling interact in ways that are not yet fully characterized.

The project is worth watching because the underlying idea is sound. Large-format 3D printing needs faster deposition strategies, and solid extrusion alone will not get there. Whether Roetz's approach is the answer or just a stepping stone toward one, it is one of the more interesting experiments in the desktop maker space right now.