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• A hierarchical toughening strategy was proposed for improving the interlaminar properties of GFRP. • The highest improvement of G IC,ini and G IC,prop values reached as much as 211 % and 174 %. • The multiscale fiber bridgings and interlaminar crossings are the key to achieve high interlaminar fracture toughness. Hierarchical toughening is commonly found in natural materials such as teeth, bone and seashells, which have evolved to withstand mechanical stresses. The incorporation of this mechanism into the design of synthetic materials, such as composites, has drawn much attention in recent decades. In this work, a carbon fiber felt (CFF) made of short carbon fibers was spray-coated with carbon nanotubes (CNT) to create a hierarchical structure that can be directly interleaved into glass fiber reinforced polymer (GFRP) composites for interlaminar toughening purpose. The results showed that the highest enhancement of G IC,ini and G IC,prop values reach as much as 211 % and 174 %, respectively, which far outweighs the state of the art. The fracture surfaces as well as crack propagation behaviors were comparatively investigated to get deep insight into the toughening mechanisms. It was found that multiscale fiber bridgings and interlaminar crossings are the key to achieving high interlaminar fracture toughness of laminate composites. [ABSTRACT FROM AUTHOR]