OptionalcategoryExpress id of the underlying IfcMaterial (or the definition itself when no nested IfcMaterial could be resolved).
OptionalnameShare of the element's volume attributable to this material, in [0,1]. Leaves of one element sum to ~1 (layer thickness / constituent fraction; equal split when no proportion data is available).
A base IfcMaterial reachable from an element's material association.