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Hello everyone (sorry if my english is not perfect),
First, I just want to say that I did researches for my problem and I didn't find any solution, so thank you if you can help me :-). I use blender 2.79b and 2.80, and the problem is the same with both : when I import an obj file downloaded from the website free3d.com, even if there is the mtl file in the same folder and the name is the same, there is no material in render mode, whatever I'm using Evee render, Blender render or Cycles render. And the materials seems to be there in the hierarchy, but when I select a material, it's just grey....
Thank you for your help]1