This paper presents a method for searching the exact rays between a Transmitter and a Receiver when a ray interacts with a material inside which multiple reflections can occur. Indeed, when considering building materials with a certain thickness, the ray-tracing algorithms often consider that the transmitted rays are not deflected, and the reflected rays are only subject to specular reflection. Therefore, the different rays lengths are not the real ones. This could be a drawback if these ray-tracings are used with a deterministic propagation modeling for UWB localization. This paper also compares the times of arrival of our method and the classical ray-tracing rays, coming from the interaction material, to estimate the possible delay and range errors.