<p>Passive thermal regulation materials offer a promising route toward energy-efficient building and smart devices. However, achieving both passive radiative cooling and solar-driven heating within a single polymeric system remains a significant challenge due to trade-offs in optical transparency, solar reflectivity, and environmental durability. Herein, we report a molecularly engineered polyimide (PI) film platform with switchable cavitation (realized through controlled cross-linking) that enables bidirectional thermal regulation. By tuning the molecular architecture, the PI films can be fabricated into either a highly porous, white reflective film for passive cooling (about 90% solar reflectivity, Δ<i>T</i> is about −6 °C) or a transparent solid film for passive heating (about 88.7% solar transmittance, Δ<i>T</i> is about +8 °C). The films exhibit excellent flame retardancy (PHRR is about 7.98 W·g⁻¹), thermal stability (<i>T</i>_max &gt; 500 °C), and environmental resistance to UV and acidic conditions. Comprehensive outdoor and simulated tests confirm their dual-mode thermal regulation capabilities. This work presents a versatile strategy for designing robust, multifunctional PI materials for year-round thermal management in extreme environments, paving the way for next-generation energy-saving polymers.</p>