Insulator/shielding in DEC power supply

I'm reconditioning some H7100A power supply units in a VAX-11/785, and I've come across something I haven't seen before. I'm hoping one of you has. :) This particular PSU was labeled 'Memory Power Supply' and has additional regulator boards for a 15v rail. Slipped between those boards were two sheets of what looked like heavy-duty paper. However, one had delaminated, demonstrating that it is a sheet of thin copper sandwiched between two paper-like layers. That suggests to me that this was intended more for EMI shielding than electrical isolation. I did not see these sheets in another PSU that also had a supplemental regulator. Does this sound familiar to anyone? TIA - Ian UNIX is user friendly. It's just selective about who its friends are. Ian S. King, Vintage Systems Engineer Vulcan, Inc. http://www.pdpplanet.org