When a partition underperforms its specification, the cause is rarely the board. It is the line where two boards meet. A butt joint between two rigid boards is a gap with a hard edge on both sides: the panels vibrate independently, the gap opens and closes with them, and the cavity behind is no longer sealed.
The H-shaped EPDM profile sits over the overlap and grips both board edges. It does three things at once. It seals the line against air movement, which is the main carrier of sound at a joint. It decouples the two boards so one does not drive the other. And it allows small movement between boards without cracking, which matters because the frame will move slightly under load and under temperature.
The material choice is not incidental. EPDM keeps its elasticity over time and does not harden into a rigid strip the way some plastomers do; a seal that hardens becomes a sound bridge. The grade used here is flame retardant to V-0 under GB/T 10707, so adding the seal does not compromise the fire performance of a non-combustible wall.
On site the detail is quick — the profile is pushed onto the board edge before the board goes in — but it has to be planned: the board layout must put the overlaps where the profile can be fitted, and the boards must be cut square. Both are drawing-stage decisions. This is the kind of 2 % cost item that decides whether a wall meets its rating.