This paper introduces an investigation on fracture mechanisms of synthetic foam sandwiches with graded multi-layered cores. The extended cohesive damage model (ECDM) is used in investigating detailed fracture mechanisms of this kind of synthetic foam sandwich panels under quasi-static 3-point bending. The ECDM prediction shows very good agreements with experimental work on investigating the sandwiches with homogeneous core and the core with four graded layers. This investigation has found that the failure modes of sandwich panels with multi-layered cores are sliding shear failure dominated fracture in the core along the path above the core-bottom sheet interface instead of pure debonding at interfaces. It has been also found an excellent mechanical performance when the core has multiple graded layers in the investigated sandwiches compared to the case of homogenous core. It is the first time that the correlation between loading capacity and number of graded layers in the core of the investigated synthetic foam sandwiches is explored. The ECDM predicted loading capacity of the investigated sandwich panel with an 8-layered core is increased by 70% compared to a homogenous core. This investigation also shows that the ECDM is a robust tool for predicting fracture mechanisms of synthetic foam sandwiches.