Hybrid aluminum/composite tubes have gained widespread utilization across diverse industries, offering enhanced performance and addressing numerous challenges associated with singular aluminum or composite tubes. However, a notable vulnerability arises during bending, as these tubes are susceptible to buckling. Specifically, when subjected to concave upward bending, the primary failure mode observed in hybrid tubes is the buckling of two parts on the compression side or upper region. This phenomenon primarily stems from delamination occurring at the interface between the aluminum and composite, induced by radial stress. Notably, debonding tends to occur under tensile radial stress conditions. To mitigate buckling, it’s crucial to induce compressive radial stress in the upper region of the tube. In this study, using FE simulation, it will be shown that the sign of the radial stress depends on the Poisson ratio along the tube axis. When the Poisson ratio of the outer composite layer surpasses that of the inner aluminum layer, positive radial stress occurs at the interface. Conversely, if the Poisson ratio along the tube axis of the composite is smaller than that of the aluminum, negative radial stress is observed. Notably, the Poisson’s ratio along the tube axis is influenced by the angle of the fiber. Using the Classical Lamination Theory (CLT), the relationship between the Poisson ratio and fiber angle was extracted. Finally, it becomes feasible to establish a threshold for predicting the sign of the radial stress.