<p>This study explores an ultrafast fiber actuator fabricated through the wet spinning of a thermo-responsive polymer, poly(<i>N</i>-isopropylacrylamide) (PNIPAM), and thermoplastic polyurethane (TPU), followed by photocrosslinking. These actuators achieve large-scale motion in under one second. Leveraging the deswelling characteristic of the thermosensitive PNIPAM above its lower critical solution temperature (LCST), reversible deformation actuation is realized, enabling the fiber to actuate in warm water and recover its original shape in cold water. Mechanical–thermal–water testing demonstrated that all fibers exhibited excellent dual thermo- and hydro-responsive shape memory properties. Notably, fibers containing 60% TPU (by mass) displayed exceptional performance, with a fixity rate of up to 86%, a recovery rate of up to 95%, and a water-responsive rate of 88%. These fibers also showed enhanced mechanical properties and thermal stability, exhibiting a threefold increase in tensile strength and a twofold increase in elongation at break compared to pristine PNIPAM fibers. Their shape memory and reversible deformation actuation remained stable even after multiple cycles, highlighting their potential applications in soft robotics and smart textiles.</p> Graphical abstract <p></p>