The acoustic infrastructure — specifically the availability and certified performance of enclosed acoustic spaces for individual focused work. This is the functional requirement that most directly determines whether employees will use the office for their most important cognitive work, or choose home instead. An office with excellent location, design, and amenities but inadequate acoustic infrastructure will see hybrid employees avoiding it for high-demand tasks. The evaluation criterion: ISO 23351-1 DS,A from an independently accredited laboratory, minimum DS,A = 25 dB (Class B), ideally DS,A = 29.4 dB as achieved by HIGHKA (SGS-verified).