Substance in Houdini is developed by SideFX Labs.

The Substance Plugin for Houdini lets you load Substance Archive files (SBARs) into Houdini in COPs. This gives you the ability to chain Substance nodes together, feed the output of Substance graphs to all parts of Houdini (Terrains, Materials, Geometry) and many other workflows. The plugin is maintained by the SideFX Labs team. 

Installation Instructions

For Houdini 17.5 the plugin is distributed with the GameDevelopment Toolset
GameDevelopment Toolset Installation Instructions

For Houdini 18.0 the plugin is distributed with SideFX Labs.
SideFX Labs Installation Instructions