WALL_SKINS_BMAT_NAMES works only in 2D. In 3D you can use WALL_MAT_A and WALL_MAT_B.
Note: when you paste codes with loops, please use other variables than “i” or “s” as these characters with brackets will be eliminated as they are interpreted as BBCodes. I changed them in your code snippets to “ii” and “ss” for a better understanding. You can read more about BBCodes here: https://gdl.graphisoft.com/forum-functions/
Gergely Fehér
Team Leader, Library Team
GRAPHISOFT SE