The hotend is usually made of a bulk heat-conductive material with an internal resistive heater, coupled with a thermistor for precise temperature control.
In common desktop 3D printer designs, the heater is located near the nozzle, and a heatsink is attached upstream (on the colder side).
[2][3] The nozzle is an interchangeable tip attached to the hotend with a small diameter hole through which the melted filament is extruded.
In desktop fused filament deposition printers, different sized nozzle holes can be used to balance between printing speed and precision.
Desired characteristics include abrasion resistance, as the nozzle frequently slides across the printed object, and thermal conductivity.