Mostly enamelled copper.
Comes in many colours, thicknesses and coil/spool lengths.
Some hints / uses / examples here.
Hand wound coils
Five different gauges and many colours.
Gauge I and II (0.20mm) and (0.315mm): 10 m / coil
Gauge III (0.50mm) (fine-medium): 2 m / coil
Gauge IV (0.71mm) (medium): 2 m / coil
Single coil, any gauge: $3.30 ($3.00)