POY (Pre-Oriented Yarn) and FDY (Fully Drawn Yarn) are both types of synthetic fibers, particularly within the polyester filament yarn category. They differ in several key aspects, including their production process, properties, and end uses.

Production Process
POY (Pre-Oriented Yarn): POY is a partially oriented yarn produced through high-speed spinning. It is an intermediate product between unoriented yarn (UDY) and fully drawn yarn (FDY). POY has a certain degree of orientation but is not fully stretched, making it suitable for further processing into other yarn types.
FDY (Fully Drawn Yarn): FDY is a fully drawn yarn produced by further stretching the POY or other intermediate yarn in a continuous process. This results in a yarn with high orientation and moderate crystallinity.

Properties
Orientation and Stability: POY has a moderate degree of orientation, while FDY is fully oriented. As a result, FDY is more stable and has less residual elongation (typically below 40%) compared to POY, which can have residual elongation above 50%.
Strength and Modulus: FDY typically exhibits higher strength and modulus due to its full orientation. POY, being partially oriented, may have slightly lower strength but retains some extensibility.
Texture: Both POY and FDY are straight fibers, but FDY's fully drawn structure gives it a tighter and more compact appearance.

End Uses
POY: Due to its partial orientation and extensibility, POY is often used as a feedstock for further processing into textured yarns such as DTY (Draw Textured Yarn). It can also be used directly in some applications where a moderate degree of orientation is sufficient.
FDY: FDY's high strength, stability, and smooth texture make it ideal for use in weaving and knitting applications. It is commonly used in the production of fabrics for clothing, home textiles, and industrial applications. FDY fabrics are known for their smooth handfeel and good dimensional stability.

The main differences between POY and FDY lie in their production processes, properties, and end uses. POY is a partially oriented yarn suitable for further processing, while FDY is a fully drawn yarn with high strength, stability, and suitability for direct use in textile applications.