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• Ultrahigh through-plane thermal conductivity achieved by continuous carbon fibers. • Thermal-induced and slant slicing-induced flexibility. • Leakage proof capacity from polymer skeleton and carbon fiber arrays. • Novel thermal management capacity from high through-plane thermal conductivity and heat absorbed during phase change. With the rapid development of micro-nano electronics, thermally conductive materials with remarkable through-plane thermal conductivity (κ ⊥) and great flexibility are greatly urgent to effective thermal management. The fillers with high thermal conductivity (TC) are commonly assembled to achieve this target. However, the imperfect contact between the joint fillers will lead to high thermal resistance (R), hindering thermal transport. Herein, we fabricated thermal interface materials (TIMs) with ultra-high κ ⊥ (up to 168.4 W m−1 K−1) and adjustable flexibility by the combination of highly thermally conductive carbon fiber bundles (CF) and polymer encapsulated phase change materials (PCMs). The alignment of consecutive CF guarantees the continuity of thermal paths, greatly facilitating thermal transport. While the slantly slicing technique and softening effect of PCMs beyond phase transition temperature lead to an attenuated compression stress (1.6 MPa@10% strain with a CF loading of 50 wt%). What's more, the latent heat absorbed by PCMs is also conducive to thermal management. Thus, during a CPU temperature-control experiment, the application of as-prepared TIMs manifests a temperature decline of 33.9 °C of CPU. This work opens a new perspective to fabricating TIMs with ultrahigh κ ⊥ and low compression stress (σ) by the combination of thermally induced flexible matrix and the slantly slicing technique of aligned CFs. [ABSTRACT FROM AUTHOR]