Low energy electron scattering processes with cage, bowl, and ring isomers of C20 are investigated employing the Dirac partial wave analysis. Rather than using a model potential to simulate the electron interaction with such isomers, we evaluate a more realistic interaction—the electrostatic potential (ESP) within a DFT framework using the B3LYP functional. A detailed collision picture is further modelled by considering several projectile–target interactions. Prominent isomer effects are observed in all the scattering observables for both the resonant as well as non-resonant scattering processes. Counter-intuitively, the ring isomer offers the maximum resonant and non-resonant collision contribution, despite having the simplest structure and the lowest electron density distribution. Different partial waves are involved in the formation of scattering resonances in the C20 isomers. Abiding to the marked differences in the cross sections, the temporal picture of the collision carries over such isomer effects distinctly. Diffraction of elastic electrons over the surfaces of cage, bowl, and ring isomers of C20 is an intriguing feature. Considerable amount of incoming flux is directed into inelastic channels at relatively lower energies leading to significant absorption effects, holding distinctively the isomer effects in such processes simultaneously.