Aluminum Sheeting
Copper Fabric
Steel Meshing
Mylar Sheeting
Aluminum and Copper Tape To Seal Up Any Leaks
Optional Items If You Want To Further Maintain Privacy From Nearby Devices That Are Connected To The Cellphone Towers Or A WiFi Router. That Have A Microphone Array Built In Like That Of A Smartphone or Tablet For Example.

Foam (Several Layers Of It For Sound Proofing)
Cellphone Jammer (A Few Small Ones)
Grounding Plate (So That The Cage Is Fully Functional)

Nice
Thanks