What are some characteristics that are good for soundproofing?

Good soundproofing materials typically have high density and mass, which help block sound transmission. They should also be flexible or porous to absorb sound waves, reducing echo and reverberation. Additionally, effective soundproofing involves sealing gaps and cracks to prevent sound leakage, ensuring a more controlled acoustic environment. Common materials include heavy curtains, acoustic panels, and soundproof drywall.