The KF 21 is a remarkable column of a coffee filter machine. Its elements are stacked so that it resembles a water tower. Costly polycarbonate plastic used to produce the crisply moulded casings gave durable and consistent glossed surfaces; the distinctive separation of reservoir and hotplate was made possible by an economically extravagant duplication of heating elements. 

The KF 21 is a revision of the KF 20, issued four year earlier with a thicker foot to accommodate a sliding thermostatic control.