Impact of common indoor materials on 77–81 GHz mmWave radar performance: signal behaviour, attenuation and reflection characteristics

mmWave radar (77–81 GHz) is gaining traction for privacy-preserving indoor sensing, yet material interactions remain undercharacterised. We experimentally quantify how common materials—wood, glass, metals, drywall, PET-G, foam and plastics—shape propagation via attenuation and non-line-of-sight (NLOS) reflections. We also benchmark key radar parameters: noise-floor levels, distance-dependent received-power trends and the agreement between measured and theoretical SNR. Metals exhibit dual effects, blocking direct transmission while producing strong reflections that enhance NLOS detection. Transparent media (glass, PET-G) support NLOS coverage, whereas foam and plastics show low attenuation and favourable penetration behaviour. From these characteristics and trends, we derive actionable, material-specific guidelines for sensor placement and multipath mitigation to improve reliability in cluttered environments. Beyond immediate use in smart homes, healthcare and security, we contribute a systematically documented experimental methodology for material characterisation and provide empirical benchmarks to refine simulation models and experimental designs. The results provides empirical insights and inform future multisignal fusion for robust next-generation indoor sensing.