The garment is a wide tunic reaching below the knee, with short wide sleeves, open down each side and fastened there with buttons or with small bells on cords. The bells are a deliberate quotation. Exodus describes the robe of the high priest as having bells of gold alternating with pomegranates around the hem, so that he should be heard when he goes into the holy place, and the sakkos takes that up openly.
Its name pulls in the opposite direction. Sakkos is sackcloth, the coarse garment of mourning and penitence, and the commentaries take the vestment as a reminder of humility and, in a common reading, of the purple robe put on Christ in mockery before the crucifixion. A garment that began as an emperor's tunic is therefore explained in church as a robe of humiliation, and both readings are offered together without either being withdrawn.
It is worn with the epitrachelion beneath it, and over it the omophorion, and with the epigonation at the side, the pectoral cross, the panagia and the mitre. In Russian practice the ensemble is heavier and more elaborate than in Greek use, and the differences between national traditions are visible at a glance in the shape of the mitre and the cut of the sakkos rather than in anything doctrinal.