Heat-setting (thermofixation)

In heat-setting, thermoplastic fibres such as polyester (PES) or polyamide (PA) are heated on a stenter frame under controlled tension. The temperature lies between the glass-transition temperature and the melting point of the fibre: typically 180–210 °C for polyester (melting point 260 °C) and 170–190 °C for polyamide 6.

Under heat internal stresses in the amorphous regions of the fibres are released, crystallinity increases and the molecular chains rearrange. On cooling the current shape "freezes" in. As a result the fabric becomes dimensionally stable, form-retaining, less prone to creasing and loses its tendency to shrink in the wash. Heat-setting is usually performed twice: once before dyeing (pre-setting to prevent dyeing distortion) and once after finishing (post-setting). Without heat-setting, PES fabrics can shrink 5–10 % during a 60 °C wash.

• Temperature: 180–210 °C for PES, 170–190 °C for PA
• Equipment: stenter frame with hot-air chambers
• Effect: dimensional stability, shrink protection, crease resistance
• Increases crystallinity, slightly reduces dye uptake