Check out the timelapses in the gallery for disolving PVA and model print.

Impossible Ball Prison

A perfect sphere, sealed inside a grid cage. No door, no seam, no gap big enough to fit it through. So how did the ball get inside?

It didn't. It was printed there.

This is a showcase — and a genuinely tough test — for water-soluble PVA support on a dual-nozzle printer. The cage and the captive sphere print in your model filament, while the whole space between them fills with PVA from the second nozzle. Drop the finished block in water, the PVA dissolves away, and you're left with a ball that rolls freely inside a prison it could never have entered.

What it actually tests

More than a party trick — it's a real torture test in three ways:

• Enclosed-cavity dissolving — the support is sealed inside the cage, so water has to work its way through the grid to reach it. Far harder than dissolving open, exposed supports.
• Support interface quality — the smoother and rounder the freed sphere comes out, the better your PVA interface settings are dialed in.
• Dual-nozzle alignment — a captive ball in a tight cage is brutally honest about nozzle offset. If your two nozzles aren't aligned, the sphere ends up off-center or fused to a wall.

If the ball comes out clean, centered, and rolls freely — your setup passes.

Printer & materials

• Printer: Bambu Lab X2D (or any dual-nozzle / dual-extruder printer with soluble-support capability)
• Model: any standard filament — PLA in the photos (main nozzle)
• Support: Bambu Lab PVA, water-soluble (auxiliary nozzle)
• Size: 50mm cube, 30mm ball
• Print time: under 6 hours on X2D using auxiliary nozzle for PVA
• Support is already assigned in the model — no manual support settings to enable.

Freeing the ball

1. Drop the printed block into lukewarm water (warm water dissolves PVA noticeably faster).
2. Let it soak — recommended at least 8 hours.
3. Change the water and give it a gentle stir now and then; fresh water and light agitation speed things up, especially for the support trapped deep in the center.
4. Rinse, dry, and enjoy your impossible ball.

Because the support is fully enclosed, give it more time and a couple of water changes versus a normal PVA print — getting water into the middle is the slow part.

Printed and tested on the X2D's dual-nozzle system, model on the main nozzle and PVA on the auxiliary. A satisfying way to confirm your soluble-support workflow is fully dialed in.