C. W. Borchert Berlin W., 58cm, 145 grams possibly late 1920s early 1930s. This Stiff Felt is from the same seller + original owner of the P. & C. Habig Wien "Special", P. & C. Habig's "Special Qualität" Reine Handarbeit Berlin Friedrichstr. 82a Soft Felt. I know Rehfus & Cie. Kehl a. Rhein was a supplier for C. W. Borchert Berlin W so could have been made by them. It has some C. G. Wilke characteristics so they could also be a possible source. The overall quality is very high and it wears comfortably.
According to this 1913 ad Rehfus & Cie (Kehl a. Rhein) made hats under the Borchert Marke.