FDY vs DTY Polyester: Choosing the Right Filament for Knit Fabrics
Fully drawn and draw-textured yarns look and behave differently on the machine: picking the wrong one is an expensive sampling loop.
The following sections cover the definition, the specification values, production control, testing and commercial impact.
How the two yarns are produced
FDY is fully drawn in one continuous process and stays flat and bright; DTY is false-twist textured to add crimp and bulk.
In practice the goal is predictability: the same result on the first order and on the fifth reorder.
Appearance and hand feel
FDY knits look smooth and slightly shiny, while DTY gives a softer, matte, more textile hand with better cover.
Specify the value on the finished fabric rather than on greige, because finishing changes almost every parameter measured.
- Request test reports on production fabric, not on development samples
- Verify the sampling plan and the number of specimens
- Store reports with roll or lot identification for traceability
Stretch and recovery behaviour
DTY contributes bulk and cover but limited stretch, so elastane is still required for four-way stretch products.
Escalate deviations immediately, as a small change early in the run is cheap to correct and costly to fix later.
Common production issues
Substituting FDY for DTY without re-development changes GSM, width and opacity, and usually breaks the fit.
Use a reference material alongside the sample so results can be interpreted if the laboratory changes.
- Agree tolerances in writing before the first sample is made
- Define the measurement condition and the direction measured
- Review the limit each season against real performance data
Selection guidance
Choose FDY for linings, meshes and crisp surfaces, and DTY for soft jerseys, fleece and brushed fabrics.
Ask for the cost of the requirement to be shown separately, so it can be weighed against the benefit it delivers.
Summary
The technical content is straightforward. The discipline lies in writing it down, testing it on production fabric and repeating the result on the next order.
