Programmable Variable‐Stiffness Multilayer Elastomer Composites With High‐Aspect‐Ratio Low‐Melting‐Point Alloy Inclusions

Variable‐stiffness soft materials are promising for robotics and adaptive systems, but phase‐change composites typically provide only binary switching with limited spatial control. Here, we introduce a programmable‐stiffness platform based on multilayer silicone laminates reinforced with high‐aspect‐ratio (HAR) low‐melting‐point alloy (LMPA) inclusions. HAR particles, produced by submerged extrusion–fragmentation, reached an effective aspect ratio of approximately 20. Using different LMPAs in discrete layers enabled layer‐wise stiffness control through composition and stacking sequence. Dynamic mechanical and isothermal tensile tests showed a strong, reversible modulus increase in the solid state and pronounced softening across the melting transition, governed by filler loading, alloy choice, and laminate architecture. Optimized Guth‐ and Halpin–Tsai‐based micromechanics models predicted stiffness with mean absolute percentage errors of approximately –, while hyperelastic fitting captured nonlinear tensile behavior with an overall error of . When integrated into a thermally addressable tendon‐driven actuator, selected laminates enabled reprogrammable deformation under identical mechanical input, with trajectory deviation increasing from at to at . These results establish HAR–LMPA multilayer composites as a scalable strategy for programming stiffness in soft matter.