Here is a recommended 'Metal' Supply Line

  
These are supply lines that are sold at local home centers.
Usually they don't meet local codes, but are available and should NOT be used!

 
Notice the 'failed' supply lines above, they may look strong on the outside
with the metal braid, but inside it's a soft flexible pipe that in this case has failed.
If the customer had installed the right kind, I probably wouldn't have been called for this repair.