Export the model as a single FBX file:
- All textures should be embedded
- 1 unit = 1 meter
- The length of the file name (including the embedded texture files) can not exceed 100 characters.
- All shaders will be automatically replaced with Unity’s “Unlit” (http://bit.ly/2hP18qx)
- Transparency for materials is not supported other than by using “glass” and “transparent”.
- For windows and other glass objects, ensure that the material name contains "glass" as a separate word, delimited by spaces, and case-insensitive.
- For transparent objects, ensure that the material name contains "transparent" as a separate word, delimited by spaces, and case-insensitive.
If your 3D editor doesn’t support media embedding, then you can use the free Autodesk FBX Converter utility to post-process your FBX and embed texture atlases into the FBX: