The next generation of electronics won’t just bend, it will stretch, deform, and conform to surfaces that were previously off-limits to circuitry. Stretchable PCBs are redefining what a circuit board can be, moving from rigid FR4 fiberglass to elastomeric substrates that flex with skin, muscle, and motion. Traditional flex PCBs use polyimide films like Kapton, which tolerate bending radii under 1mm but fail catastrophically under tensile strain. True stretchable circuits demand a fundamentally different approach, treating mechanical compliance as a design parameter rather than a constraint. Three strategies dominate the field: • Serpentine geometries: Copper or gold traces are patterned in horseshoe or sinusoidal shapes, allowing the conductor itself to unfold under strain. The metal never stretches, the geometry does. Properly engineered serpentines can survive 30-50% biaxial strain across thousands of cycles. • Liquid metal conductors: Eutectic gallium-indium (EGaIn) and Galinst...