What kinds of materials make good sound insulators?

Materials that have high density and low elasticity are typically good sound insulators. Some examples include:

1. Cork
2. Fiberglass
3. Foam
4. Rockwool
5. Mass-loaded vinyl
6. Acoustic panels
7. Acoustic fabrics
8. Soundproof curtains
9. Rubber
10. Insulating foam boards

These materials are able to absorb and dampen sound waves, reducing noise transmission and creating a quieter environment.