The direct 3D printing of investment shells and sand castingCasting molds offers substantial opportunities to streamline the production process for low-volume, high-complexity aluminumAluminum castingsCasting, particularly for aerospaceAerospace and military applications. Nevertheless, a thorough modeling and thermal mapping of the shells and the molds are necessary given that the thermomechanical characteristics of these materials are not well understood. Here, we demonstrated the employment of the novel Rayleigh Backscattering-based fiber-optic sensors for real time, distributed measurementMeasurements of temperature with higher spatial resolution within various 3D-printed shells and molds during laboratory trials of an AA356 aluminum alloyAluminum alloy. The optical fiber technology-enabled distributed temperature measurementTemperature measurement within the mold and molten aluminumAluminum during the pouring and solidificationSolidification processes, offering a spatial resolution of 0.65 mm for temperatures up to 800 °C. The capability to differentiate between closely spaced temperature variationsVariations, which generates detailed and information-rich thermal maps, unlocks numerous applications within additive manufacturingAdditive manufacturing.