• The hierarchical CoNi@SnO2@Sn heterostructure achieves a minimum reflection loss of −62.29 dB and an effective absorption bandwidth of 2.2 GHz, fully covering the C-band at a thin thickness of 2.61 mm.
• The magnetic–dielectric synergy, enabled by CoNi nanosheets and Sn/SnO2 interfaces, enhances impedance matching and attenuation, overcoming the low-frequency absorption bottleneck.
• The CNS/TPU composite film exhibits superior low-frequency microwave absorption (RLmin of −61.04 dB, EAB of 2.5 GHz) and improved thermal conductivity (2.41 W m−1 K−1 in-plane), making it suitable for flexible electronics.
• This work provides a novel strategy for designing 1D metal-based absorbers with strong magnetic–dielectric synergy, advancing applications in 5G communications and EMI shielding.