2. What is the included cable made of? Is the cable interchangeable?

[Material of included cable]
The FD3 comes with a 4-stranded 120-core Litz braided high-purity monocrystalline copper cable with a 3.5mm plug.
The FD3 Pro comes with an 8-stranded 152-core Litz braided high-purity monocrystalline silver-plated copper cable with interchangeable 2.5mm, 3.5mm and 4.4mm audio plugs.

[Is the cable interchangeable]
The cable of the FD3 is detachable with a standard MMCX connector. (Compatible with FiiO's cable series with a detachable MMCX connector, including the LC-2.5/3.5/4.4B, LC-2.5/3.5/4.4C, LC-2.5/3.5/4.4D, LC-RE, LC-BT1, LC-BT2, UTWS1, UTWS3 and IRC-MMCX.)