The regular Doepfer 19-inch Euro-rack system has a usable width of 84 HP. If the modules you install don’t use up the entire 84 HP, you are advised to cover up the empty spaces with blanking panels due to safety and EMC reasons.
As i wrote in an earlier blogpost, the (static) electricity from the system causes the A-100 to be a real dust-magnet.
Blind Panels are available in the following sizes;
A-100B1 : 1 HP
A-100B2 : 2 HP
A-100B4 : 4 HP
A-100B8 : 8 HP
A-100B42: 42 HP
A-100B84: 84 HP
Doepfer also sells the A-100B1.5, a 1.5 HP wide blind panel that for example fits the Analogue Solutions modules together with eurorack modules of other manufacturers.