<p>The band structure and wave attenuation characteristics of a folded hybrid composite metabeam are investigated using the spectral element method. The metabeam comprises periodically arranged segments of aluminum and a three-phase hybrid composite, which is reinforced by unidirectionally aligned carbon fibers and thickness-wise graded graphene platelets (GPLs). The effective material properties of the hybrid composite are determined via a hierarchical homogenization scheme. A refined spectral element formulation is developed to derive the dispersion relations of the periodic structure. A comprehensive parametric study reveals that the folding angle plays a dominant role in shaping the continuity and width of bandgaps. In contrast, the weight fraction and distribution pattern of GPLs, and the volume fraction and orientation of carbon fiber primarily shift the bandgap frequency locations without compromising the attenuation level. Moreover, the coupling between geometric folding and material anisotropy is crucial for achieving stable and broadband attenuation. Frequency responses of finite folded metabeams demonstrate that strong bandgaps produce distinct attenuation regions, whereas weak counterparts can be obscured by resonances. The present work provides a guideline for the design and tuning of folded composite metabeams with enhanced wave attenuation performance.</p>