Heat setting
Also searched as: heat-setting, thermosetting, stenter setting, tenter setting, presetting, steam setting, autoclave setting
Heat setting stabilizes thermoplastic fibers, yarns or fabrics by heating them above their glass transition temperature in a chosen shape and then cooling, so shape and dimensions persist in later use.
In detail
Thermoplastic fibers such as polyester and nylon carry internal stresses from drawing, texturing, knitting or weaving, which cause shrinkage or distortion when they are later heated. In heat setting the material is held at defined dimensions, for example pinned on a stenter frame for fabric or wound in packages in an autoclave for yarn, and heated with hot air, contact heat or steam. Chain segments gain mobility, stresses relax and the crystalline structure reorganizes; cooling below the glass transition then locks in the new configuration. The same principle sets texturing crimp and permanent pleats.
The science and numbers
Setting temperatures must lie above the glass transition temperature (Tg), where amorphous chain segments become mobile, and below the melting point, where the oriented structure would be lost; for PET, Tg is about 75 C. A review of melt-spun fibers describes annealing under strain, or heat setting, as partially relaxing frozen-in stresses from drawing and perfecting and stabilizing the microstructure, so shrinkage on later heating falls. A set is generally stable against later exposures below the highest effective temperature the fiber has experienced. Water plasticizes polyamides and lowers their effective Tg, which helps explain why steam and hot-wet conditions are effective for setting nylon. In false-twist texturing of polyester, heater temperatures around 200 C and above are reported for setting the twisted configuration.
A practical example
A knitter of polyester and elastane sportswear finds that unset fabric curls at the edges and shrinks unevenly in dyeing. After the greige fabric is pinned on a stenter at its target width and passed through a hot chamber, it lies flat, holds its width through dyeing and keeps its dimensions after home laundering at ordinary temperatures.
What to distinguish
Heat setting applies to thermoplastic fibers; cotton, wool and viscose are not heat set in this sense, and wool is set with moisture, heat and chemistry instead. The set holds only below the setting temperature, so ironing or drying hotter than the set point can undo or distort it. Excess temperature can yellow, stiffen or glaze fabric and weaken elastane.
Origins and history
Heat setting became essential once melt-spun synthetics reached textile mills in the mid-twentieth century, beginning with nylon from Wallace Carothers's polymer research at DuPont and followed by polyester. Producers found that these thermoplastic fibers could be given a lasting shape by heat, enabling dimensionally stable knits, durable pleats and textured stretch yarns. It remains a routine step in finishing synthetic wovens and knits and in processing carpet yarns, placed before or after dyeing depending on the fabric.
Related terms
Sources & further reading
- Materials: Melt-spun fibers for textile applications (Hufenus et al., 2020)
- Polymers: Hygromechanical behavior of polyamide 6.6, experiments and modeling (Wetzel et al., 2023)
- Preprints.org: A review on false-twist texturing
- American Chemical Society: Foundations of Polymer Science, Wallace Carothers and the development of nylon
Technical references reviewed 2026-09-22. Examples are illustrative. Industry organizations and manufacturers describe their own fields; their references are not independent product endorsements. Figures are approximate and depend on the stated test conditions.