Magnesium hot foil print plate.
Magnesium print plates are created using a chemical/UV etching process. They can hold very fine detailing and are fairly affordable, but the magnesium is quite soft and can be easily damaged.
Brass hot foil print plate.
Brass print plates are CNC engraved and can hold fine detailing, they also have a steeper etching angle making them better for printing pigment (coloured) foils.
They are more expensive to produce, but are more durable.