Hi

Following along Jeff's webinar on material Style sheets, right about the 1 hour mark there is a demo applying a material Style sheet to a packed primitive.
To better my understanding, I'd like to know why it doesn't work (both in the webinar and my sample .hip file)

My hip is attached.

Since you aren't assigning the material with a stylesheet, mantra only knows about the materials on the geometry or on objects. Since the geometry is packed, it can't ‘see’ the materials on the geometry either. Therefore none of the materials in the scene are sent to the render. You'll need to force the inclusion of the materials by setting declare materials to ‘declare all materials.’

Hope that helps