It's the minimum thickness of each layer that is printed. (geekwrapped.com)
The exact thickness of that layer is unknown, but as it gradually cools, it should form solid chunks that sink like iron snow into the denser, solid inner core, also of unknown size, says geophysicist Sean Solomon of the Carnegie Institution of Washington's Department of Terrestrial Magnetism, the mission's principal investigator. (scientificamerican.com)
Thickness of layers shown here is not to scale. (sciencedaily.com)