Hello,
Excuse-me if this this question was already asked in this forum, but I didn’t find it with the search engine.
I use Blender to create 3D objects at OBJ format, then use them in Sweet Home 3D a free interior design application I developed.
Even if the “Double Sided” button in Mesh panel is checked, I never get double sided meshes in the OBJ file. What should I do ?
Note that I would prefer not to duplicate objects and flip their normals. 
Thank you for your help.