What characteristic is unique to filament used in Fused Deposition Modeling (FDM)?

Filament used in Fused Deposition Modeling (FDM) is typically a thermoplastic, which means it becomes pliable or moldable upon heating and solidifies upon cooling. This characteristic is crucial for the FDM process, as the filament is extruded through a heated nozzle that melts it, allowing it to be deposited layer by layer to build a 3D object. After the printing is complete, the filament cools and solidifies to form a stable structure.

The requirement for the material to be a thermoplastic ensures that it can be repeatedly softened and reshaped, which makes it ideal for the FDM process, where precise control over the material flow and shaping is necessary. This unique property sets it apart from other materials used in different additive manufacturing techniques, leading to the prevalent use of thermoplastic filaments like PLA, ABS, and PETG in FDM printers.