The hotend is the heated assembly of an FDM 3D printer that melts thermoplastic filament and forces it through a nozzle, comprising a heater block, heat break, heat sink, and nozzle.
In fused deposition modeling (FDM) 📝3D Printing, the hotend performs the core function of material extrusion: it raises filament above its melting point so the polymer can be deposited layer by layer. It is typically divided into a hot zone and a cold zone. The hot zone centers on a heater block, which houses a resistive cartridge heater and a thermistor or thermocouple that together hold a precise target temperature, commonly between 190°C and 260°C depending on the material.
Heat is confined to this zone by the heat break, a thin-walled tube—often stainless steel or titanium for their low thermal conductivity—that mechanically joins the hot and cold sides while limiting heat from traveling upward. Above it, a heat sink and cooling fan dissipate stray heat to prevent heat creep, in which softened filament expands and jams the filament path before reaching the melt zone.
At the base of the hotend, the nozzle forms the final aperture through which molten plastic is deposited. Hotends are broadly classed as all-metal or PTFE-lined: all-metal designs tolerate the higher temperatures required by engineering materials, while PTFE-lined designs are simpler but capped by the tube's thermal ceiling. The hotend is distinct from the extruder, the separate mechanism that drives filament into it.