Default [Teardown] What is the material on the shielding covers ?

Dear all,
I have spent some time disassembling my Nexus 5 and I found that the shielding cover that faces the die-casting has a strange "gold" tape on it (cf. picture enclosed).

I am curious, does anyone know what is it ? Is it a "high" thermal conductivity material that send the heat to the die-casting ? Or is is electrically non-conductive material that avoid leakage ?

I am a bit concerned because if it is for heat transfer, why not putting something on the CPU too ?

Thx for your feedbacks.
Attached Images
File Type: jpg shielding.jpg - [Click for QR Code] (172.5 KB, 476 views)