Open structure is essential: Materials like rockwool, fiberglass, and acoustic foam absorb sound by allowing air to enter their pores. The sound energy is dissipated as heat through friction and viscous losses.
Density matters—but not linearly:
Too low: Air passes through without much resistance → poor absorption.
Too high: Air can’t penetrate → reflects sound instead of absorbing.
Optimal range: Depends on frequency. Lower frequencies need thicker and denser materials; higher frequencies are absorbed by lighter, more porous ones.
Airflow resistivity: This is the real MVP. It measures how much the material resists air movement. Ideal absorbers have moderate-to-high airflow resistivity, which correlates with effective sound damping