So, here's something that might add to this discussion from a prominent researcher engaged in another forum, Dan Sharp has written and researched the Horten subject extensively and has had his results published before, which I've referred to in the past in my assertions that Horten didn't apply LO technology in the construction of their flying wing. This is what Sharp recently stated about the subject based on recent research he's done:
"In September 1944, Professor Dr Kurt Krüger, director of the Institut für Luftfahrtgeräte der Technischen Akademie der Luftwaffe at Berlin-Gatow and the Messtechnisches Institut, Königshofen im Grabfeld, produced a report entitled Reflexion elektromagnetischer Wellen an Flugzeugbaustoffen - Reflection of electromagnetic waves on aircraft building materials.
The report summary says: "The task is to camouflage planes and other flying objects against exposure to radio measuring devices, i.e. to make the reflection amplitude of the aircraft as small as possible. In the present report, it is proposed to solve this problem by preferably building the aircraft out of electrically permeable substances and by covering those components that must be metallic in nature (such as the engine, landing gear, etc.) with electrical absorbing substances."
The report notes that "through the mediation of the OKL and their own efforts, materials such as Tronal, Atex, plywood and a combination of several building materials were procured and measured by various companies". One of those companies was Gothaer Waggonfabrik, which at the time was engaged in building the Horten 8-229 prototypes. There is a diagram of a generic twin-engine flying wing aircraft included in the report with the caption "Nurfluegler mit schluckstoffverkleideten (schraffiert gezeichnetan) metallischen Bauteilen." - "Flying-wing aircraft with metallic components clad with absorption material (shown hatched)." The hatched area covers where the engines would be, the cockpit and the undercarriage.
Evidently Gothaer was trying different sets of layered material to various thicknesses which included plywood, Moltopren (a sort of plastic foam, I think), cellular rubber (Hartzellkautsch) and what is described as Holzgitter - wooden lattice.
This report doesn't overtly say 'there was a plan to make the 8-229 out of radar absorbing materials', but it does clearly show that radar absorbing materials were being considered for flying wing types and that Gotha was involved in testing those materials during the same time period when it was building 8-229 type flying wings. The Hortens were working closely with Gotha and would almost certainly have been aware of Krüger's work. Of course, Krüger, his colleague Dr H. G. Grimm (who was managing the materials testing) and the institutes were left out when Reimar Horten mentioned the radar absorbing material to David Myhra during his interview.
Krüger himself was evidently killed before the end of the war, according to a CIOS evaluation report I have.
This says that development of his absorbent materials was at an early stage, which may well mean that they hadn't yet been applied to an actual aircraft.
So although Horten wasn't necessarily telling the whole truth, I don't think he was really lying either."
This comes from the excellent Secret Projects forum, of which he's a regular contributor because of the research he's done:
Hi! Wing cross section of Horten Ho-Ⅸ.