public void SetMaterialIdForCurrentExportState(
	ElementId elementId
)

Public Sub SetMaterialIdForCurrentExportState ( _
	elementId As ElementId _
)

public:
void SetMaterialIdForCurrentExportState(
	ElementId^ elementId
)

Even though there could be several materials associated with the element (set during PushExportState()), unless the element has support for IfcMaterialLayerSet, IFC output will include only this one.