All NSL:EI materials are stored under the Assets folder in NSLEasyInteriors/WallParts/Resources/Materials. There is a folder for each material type.
These are standard materials and can be modified using your own selection of shaders. To add your own custom materials, use an existing texture as a template (NSLEasyInteriors/WallParts/Resources/Textures) and create a new material in the appropriate folder (e.g., to add a new Floor material, create a new material in, or copy a material to NSLEasyInteriors/WallParts/Resources/Materials/Floor). If you have an NSL:EI window open, you will need to close it and open a new window to see your new materials in the designer.
Door and Window materials are not applied in the NSL:EI window. To apply these materials, simply select the windows or doors you would like to change in Unity’s object hierarchy (under your floorplan name) and apply materials as you normally would in the inspector. Windows and doors each have child objects which can have different materials applied to each.
To have your own prefabs available for use inside NSL Easy Interiors, simple copy or create standard Unity Prefabs in the NSLEasyInteriors/WallParts/Resources/EIPrefabs folder. If you have an NSL:EI window open, you will need to close it and open a new window to see your new prefabs in the designer.