This 3D-printed Christmas tree made out of ice was created by researchers at the University of Amsterdam in the Netherlands. The system makes use of the same evaporative cooling effect used by some temperature control units. Under a vacuum, water evaporates at much lower temperatures than normal, with each molecule transferring a small amount of heat away from the remaining water reserve. This means that the liquid water becomes colder and colder until it is supercooled.

The printer uses an ultrathin stream of this supercooled water as ink, which freezes as soon as it hits previously formed ice. This allowed the researchers to build the tree layer-by-layer, completing the 8cm-tall tree in just under half an hour. The researchers say that there could be practical applications for this technology, such as printing sacrificial scaffolds for tissue engineering or forming intricate channels for a microfluidics network.