WW2 German officers breeches or trousers

[PBaczuk]

I found these trousers yesterday, they are not wool but are a nice deep grey green (field grey) and RBN 0/0250/2323 stamped. They are missing all fly buttons. The bottom inside of the trousers legs have a black material as seen in the images. I tried to capture the weave of the material because it is not HBT and the trousers are not wool.