<p>Stretchable encapsulation has evolved from a passive protective layer to an active, multifunctional interface with the advancement of flexible electronics, wearable devices, and bio-integrated systems, and it is critical for ensuring device performance, long-term stability, and biological safety in dynamic, humid, and bioactive environments. Addressing the core “mechanical performance-barrier performance” trade-off in stretchable polymers, this review focuses on seven polymer families (silicones, polyolefins, polyacrylates, polyurethanes, polyesters, fluoropolymers, hydrogels). It analyzes how molecular architecture, cross-link density, and filler/interface engineering synergistically define key material attributes, and employs representative sensing display, and energy storage devices to illustrate encapsulation failure mechanisms under cyclic strain, humidity, and body fluids. Finally, it outlines design principles for achieving stretchability, high reliability, and environmental compatibility stretchable encapsulation materials, offering a foundational reference to advance their integration into flexible and bioelectronic technologies.</p>