Actual substantive objects, such as solids, liquids, gasses, etc. are material. All such objects can be understood objectively. If something exists that cannot be known objectively, then this would be immaterial. It seems logically necessary that such a substance would have to be ontologically distinct from the material. For example, the soul, if it exists, could not be knowable objectively but possibly could be knowable through introspection.
This concept is very similar to the concept of physical/nonphysical.