From what I have seen, the insulation parameters are not exposed in the Revit API. We had a programmer write out the values to custom fields to help us out.
Not the answer you are looking for but there is another way until you get that resolved: Fabrication Reports
Select the item(s), in the modify menu look for Fabrication Exports, pick Export Fabrication Data
These are built using old reports in Autocad Fabrication but can be done in Revit as well. Export is a CSV file. I have attached an example with the standard program defaults