ABSTRACT Developing fiber actuators with both complex deformability and precise programmability remains a critical challenge in smart textiles and soft robotics. Inspired by the segmented structure of earthworms, we actively guide the Plateau−Rayleigh instability to fabricate microfibers with a segmented core in a sodium alginate (SA)/polydimethylsiloxane (PDMS) shell‐core structure. The off‐center distributed core and differential hydrophilicity enable rapid, reversible water‑actuated bending w