He was one of the founders of the school of physics at the University of Ljubljana and a prominent member of the international research group in the field of transport theory, contributing to the theoretical aspects of the diffusion of light, neutron science and dynamics in rarefied gases.
Later Kuščer coauthored two university textbooks, on thermodynamics[4] with S. Žumer, and on mathematical physics[5] with Alojz Kodre, also published in German by Springer.
His early research was on classical radiative transfer using the Boltzmann equation because of his interest in the optics of underwater light fields: this was also the theme of his doctoral dissertation.
In later research, he turned to solving classical one-dimensional transport problems for radiative transfer, including polarized light and thermal neutrons, using the Boltzmann equation.
[11] At the home faculty, the graduate lecture hall is named Kuščer seminar, decorated by a sketch by a Slovenian caricaturist Božo Kos.