<p> Achieving highly linear and sensitive strain sensing under both tensile and compressive deformation remains a critical challenge in wearable electronics, as it demands a conductive network capable of reversible reconfiguration without compromising structural uniformity. This challenge is further intensified in hierarchical carbon nanostructures, where catalyst deactivation and unregulated carbon supply frequently lead to nonuniform nanocarbon growth and severely heterogeneous conductive pathways. Herein, we report a hierarchical carbon aerogel derived from plastics. Carbon nanofibers (CNFs) are in situ grown on elastic carbonized cotton fibers via plastic pyrolysis, enabled by Ni–S-modified catalytic interface and sustained carbon flux from plastic decomposition. The coupled regulation suppresses uneven nanocarbon deposition, yielding an elastic fibrous backbone densely interconnected by CNFs. The resulting network facilitates reversible reconstruction of conductive contacts under tension and compression, delivering a nearly linear electromechanical response over a broad bidirectional strain window with linear gauge factors of 7.8 at 82% tension and 1.7 at 28% compression, while maintaining stable sensitivity over 5000 cycles within a ± 20% strain window. Overall, this work achieves a wide bidirectional strain range, high sensitivity, and long-term stability, rarely combined in carbon-based strain sensors. Moreover, it reliably resolves strain direction and magnitude, enables sensitive adhesion sensing and joint-motion monitoring, highlighting its potential for next-generation human–machine interfaces.</p>