The investigations presented in this article include a comparative study of static and fatigue four-point flexural tests performed for sandwich composites. The investigated composites consisted of a glass-epoxy laminate as a cladding material and core materials, such as synthetic foams and natural cork agglomerates, in different densities. The sandwich composites were prepared with the vacuum bagging method using the same resin, reinforcement, and additives. Although using cork agglomerate in sandwich composites instead of synthetic foam resulted in a decrease of the static flexural strength in such composites, it increased their resistance to fatigue cycles considerably and benefitted their eco-friendly image. However, only the reproducibility of all the factors in the production process and testing of composites allows a direct comparison of their test results to be made.