diff --git a/cymetric/metrics.py b/cymetric/metrics.py
index 3cf56d5..c798668 100644
--- a/cymetric/metrics.py
+++ b/cymetric/metrics.py
@@ -115,13 +115,14 @@ def materials(rsrcs, comps):
     Resources times the massfrac in Compositions) indexed by the SimId, QualId,
     ResourceId, ObjId, TimeCreated, and NucId.
     """
+    rsrcs = rsrcs[['SimId', 'QualId','ResourceId', 'ObjId', 'TimeCreated',
+                   'Quantity', 'Units']]
     x = pd.merge(rsrcs, comps, on=['SimId', 'QualId'], how='inner')
-    x = x.set_index(['SimId', 'QualId', 'ResourceId', 'ObjId', 'TimeCreated',
-                     'NucId', 'Units'])
-    y = x['Quantity'] * x['MassFrac']
-    y.name = 'Mass'
-    z = y.reset_index()
-    return z
+    x['Mass'] = x['Quantity'] * x['MassFrac']
+    x = x.drop(['Quantity', 'MassFrac'], axis=1)
+    x = x.reindex(columns=['SimId', 'QualId', 'ResourceId', 'ObjId',
+                           'TimeCreated', 'NucId', 'Units', 'Mass'])
+    return x
 
 
 del _matdeps, _matschema