Is there an easy way to assign a substance material in Houdini asset and then have it show up in Unreal? I am using the Substance plugins for Houdini and Unreal, but they aren't talking to each other.

Right now, I can assign basic textures from in Houdini, but substances just show up blank. Maybe i need to somehow embed the substance in the OTL?

You can use an Attribute Create Node in which you can assign any unreal material to your digital asset.
Just enter unreal_face_material in the name field, change class to primitive, type to string and enter your
unreal materials path (you can copy the link in unreal by right clicking the unreal material and choosing copy reference).

You can also promote this field to your user interface, so the user can change the material later.

thank you! that is a big help!

Is there a list, somewhere, of special attributes like this for the Engine?

I didnt found one yet. But i just started using Houdini, so perhaps one of the official houdini people can post a link.

I've also tried the unreal_instance attribute as mentioned here https://www.sidefx.com/forum/topic/46689/ [sidefx.com]
got the same bug that the assets where invisible during gameplay. but, when baking out everything works and was instanced correctly.

Concerning the substances I think both methods could make sense.

When asigning the substances in houdini as you mentioned, i think the substance parameters could get controlled from the interface, so each placed asset (in unreal)could have its own texture set.
Advantage of using the substances in unreal is, that they could get reused instanced and manipulated for every other unreal asset as well which might safe some performance.
The nonplusultra might be a combination of both methods, using the substances in unreal, editing the materials to use dirtlayers or any other overlays and generate dirt and alphamaps in houdini.