An example of an object that does not reflect any sound is an anechoic chamber.
An anechoic chamber is a specially designed room or chamber that is constructed with materials that absorb sound waves instead of reflecting them. The walls, ceiling, and floor of the chamber are typically covered with sound-absorbing materials, such as foam wedges or specially designed panels. These materials are designed to minimize sound reflections by converting sound energy into heat or dissipating it.
When sound waves encounter the surfaces of an anechoic chamber, they are absorbed rather than being reflected back into the room. This absorption eliminates or greatly reduces echoes, reverberations, and reflections, resulting in an environment with extremely low sound levels. As a result, it creates a space where sounds appear to be absorbed almost completely, giving the impression of "soundlessness."
Anechoic chambers are often used for scientific and engineering purposes, such as acoustic research, audio testing, or studying the sound characteristics of objects or devices in an environment with minimal sound interference.