Depending on the degree to which the materials absorb sound waves, we can speak of absorbent or reflective materials. Absorbent materials are those that absorb most of the sound waves that impact their surface. Reflective materials, on the other hand, absorb little of these sound waves. If an enclosure is made of reflective materials – glass, mirrors, polished surfaces – the sound waves generated inside the enclosure will be reflected excessively, producing reverberation: at the slightest activity inside the enclosure, a sensation of amplified sound will be generated, like the bustle generated by diners in a bar.