The cover plate 3DE should only apply a light pressure on the soft insulating material: the knobs (protected design) must therefore be tightened lightly.
The cut edge of the insulation is covered by the cover plate and offers a pleasing appearance.
The inside cover guarantees the air-tightness of the access door: the knobs must therefore be fastened firmly.
The air pocket trapped between the cover plate and the access door offers good insulating properties.To avoid any convection currents insulation chunks can be stuffed into the hollow spaces between the cover plate and the access door.
To maximize the range of possible insulation thicknesses, steel knobs (they are less bulky than the plastic ones) are used.