the main thing you want to look at when comparing 'acoustic' plasterboard is the surface density (kg/m² ), the higher the number the more mass it has and better it performs and a mass barrier   From what i can see 12.5mm GTEC dB is 10.2 to 10.7 kg/m² , and 15mm is 12.5 to 13.1 kg/m².   other boards as below;   Gyproc wallboard                          12.5mm - 8.0 kg/m2, 15mm - 9.8 kg/m2 Gyproc fireline                                12.5mm - 9.8 kg/m2, 15mm -