diff --git a/src/SimNDT/core/materialLibrary.py b/src/SimNDT/core/materialLibrary.py
index 4cce50e..66cfa66 100644
--- a/src/SimNDT/core/materialLibrary.py
+++ b/src/SimNDT/core/materialLibrary.py
@@ -24,7 +24,7 @@ def CC(x):
 
 def getMaterialLibrary():
     MaterialList = list()
-
+    # rho, VL, VT
     MaterialList.append(CC(['air', (1.24, 344, 1e-30)]))
     MaterialList.append(CC(['aggregates', (2600, 5751, 3282)]))
     MaterialList.append(CC(['aluminium', (2720, 6320, 3772)]))