Will blown-in fibreglass settle?

No, not if the fibreglass is installed at the correct design density. Certified blown-in fibreglass contractors are required to do density tests in every application (generally every 600 feet). Caution should be taken if cellulose is used in the blown-in fibreglass because it will settle. Thermo Seal will not install Cellulose in blown in applications or attics because it settles and reduces the R-value. Blown-in fibreglass won’t settle from gravitational forces or household vibrations such as slamming doors. CCMC reported after a simulated drop test (60 times from a height of 2.5 cm) that there was no settlement.