diff --git a/atomrdf/network/ontology.py b/atomrdf/network/ontology.py
index 46e35d4..4cb2504 100644
--- a/atomrdf/network/ontology.py
+++ b/atomrdf/network/ontology.py
@@ -84,6 +84,7 @@ def read_ontology():
     #CMSO -> PODO IMPURITY
     combo.add_path(("cmso:Material", "cmso:hasDefect", "podo:SubstitutionalImpurity"))
     combo.add_path(("cmso:Material", "cmso:hasDefect", "podo:InterstitialImpurity"))
+    combo.add_path(("podo:InterstitialImpurity", "rdfs:label", "string"))
     combo.add_path(("cmso:AtomicScaleSample", "podo:hasNumberOfImpurityAtoms", "int"))
     combo.add_path(("cmso:AtomicScaleSample", "podo:hasImpurityConcentration", "float"))
     
diff --git a/atomrdf/structure.py b/atomrdf/structure.py
index 0ca136d..a328569 100644
--- a/atomrdf/structure.py
+++ b/atomrdf/structure.py
@@ -1065,11 +1065,14 @@ def add_interstitial_impurities(
             )
             json_io.write_file(outfile, datadict)
 
-            self.add_triples_for_interstitial_impurities(conc_of_impurities, no_of_impurities=no_of_impurities)
+            self.add_triples_for_interstitial_impurities(conc_of_impurities, no_of_impurities=no_of_impurities, label=void_type)
         return sysn
 
-    def add_triples_for_interstitial_impurities(self, conc_of_impurities, no_of_impurities=None):
-        defect = self.graph.create_node(f"{self._name}_InterstitialImpurity", PODO.InterstitialImpurity)
+    def add_triples_for_interstitial_impurities(self, conc_of_impurities, no_of_impurities=None, label=None):
+        if label is not None:
+            defect = self.graph.create_node(f"{self._name}_InterstitialImpurity", PODO.InterstitialImpurity, label=label)
+        else:
+            defect = self.graph.create_node(f"{self._name}_InterstitialImpurity", PODO.InterstitialImpurity)
         self.graph.add((self.material, CMSO.hasDefect, defect))
         self.graph.add((self.sample, PODO.hasImpurityConcentration, Literal(conc_of_impurities, datatype=XSD.float)))
         if no_of_impurities is not None: