Knopp Ferro creates sculptures made of metal that are referred to in catalogs and texts as "room sculptures" and "installation sculptures"; both are apt. They are mobile-like structures, composed of a multitude of wires holding metal rods and connected by them at the same time. Forming the body of the standing or hanging sculpture, they are usually fixed at one point and precisely balanced. Despite their weight, they seem to float almost weightlessly. Seeming to follow an organized system, the horizontal and vertical planes alone define their shape. However, this impression is fleeting. With every movement that affects it–be it a draft or people in the room–the image that is supposed to be recognizable disappears and gives way to a new one. Nothing is as it seems, and the viewer  continually discovers a new picture. The constant change questions and relativizes our habits of perception.

Depending on size and production, all works are divided into sub-groups, for example "liners", "Color Space", "fugue", "line field", "system" and "prob". Every group now comprises a large number of works.

The titles all correspond to the time the works were completed, a completely neutral name that does not invite hasty associations. Knopp Ferro leaves this to the viewer. By this means, in addition to the three spatial dimensions, the fourth dimension of time is integrated into the work.

If the early works, such as those in the Trinitatiskirche in Cologne, are still understated and simple in form and color, the sculptures become more comprehensive over time. In addition to the increasingly complex, technically sophisticated form,  color also begins to figure more prominently.