In some render engines like Twinmotion and Lumion, only one side of a Rhino surface with a material may be shown. To display the material correctly on both sides, you need to check a box called “2-sided” to flip the normal.
The question is whether there is a way to set this in Rhino directly, without needing to set up 2-sided material ?
Hi @p.pec
Not really, because it’s up to the render engine if they want to render the backfaces - it’s not a geometrical property. What you can do to avoid having to turn on 2-sided in the render engine is to give you geometry actual thickness using Offset (or OffsetMesh if it’s mesh objects), so that your geometry has no (visible) backside. No such thing as zero-thickness materials exist in the real world anyway 
-Jakob
As Jakob points out and you are already aware, forcing a two sided material OR providing the render engine with geometry that has physical thickness is your only real option.
Some rendering engines, such as Enscape, will treat everything as 2 sided and with a program like SketchUp where you can paint two sides of a 0 thickness surface with different (or the same) materials, Enscape will render this as if 2 sided by default and actually without the option to disable this if I remember correctly.
A hacky solution that I wouldn’t really recommend is that you can copy & paste your 0 thickness surfaces in the same exact place and just flip the normals on the copy, then inside of the rendering engine such as TM you will see your material on both sides of it because you have outward facing normals on both sides (but now you have double the geometry, and overlapping geometry at that)
ahah that sure! thanks
ah thanks i didnt know that about Enscape! thanks