The team used Substance Painter, Photoshop, Houdini and FumeFX to generate VDB data. You can watch the trailer on YouTube.

The team used Substance Painter and Photoshop for the surfacing and texturing work, also implementing Blender paint tools for the balance. As for Houdini and Fume FX, artists used them to generate VDB and Alembic data for import and render in Cycles.

Stefan Werner and Luca Rood (some of the artists behind the project) are said to have worked on adding proper support for VDB voxel data, and improving the Alembic support, importation and exposing attribute data for use in Cycles material networks included.

You can learn more here.