For conditioning build material for fused filament fabrication, thermal power is both added to and removed from a nozzle in a manner that can reduce sensitivity of the nozzle temperature to fluctuations in build material feed rate. The amount of thermal power added is at least as large as the sum of the amount removed, the amount to condition the material, and losses to the environment. The amount removed may be at least as large as half the thermal power required to condition the material to extrusion temperature, and may be comparable to, or much larger than the conditioning amount. The larger the ratio of the amount removed to the conditioning amount, the less sensitive the nozzle temperature will be to fluctuations in build material feed rate. Fine temperature control arises, enabling building with metal-containing multi-phase materials or other materials that have a narrow working temperature range.