Why import is missing some of the faces?

I am importing attached obj file. It is a rectangle with material on both the faces, exported from Sketchup.
TriangulatedModel.mtl (329 Bytes)
TriangulatedModel.obj (417 Bytes)

Why one of the face is missing when importing it in Blender ?

It’s a rectangle, there is in fact only 1 face, if the material is applied to either side, you need to create a shader tree which accounts for this. I also realigned the UVMap to fit within the UV space.

Backfacing.blend (1.1 MB)

I am using Blender to reduce/decimate the polygon through python scripts.
How could I make sure if there is a backface then material is applied to it through scripts ?

Also if I export it to obj then backface information is lost. Both triangles and material applied to it.

That would make sense, (the losing the materials), as each software would handle backfacing in it’s own fashion. It’s the same when importing, even if you are using UV Maps and images, you still need to build the material. No avoiding that I’m afraid, the closest you get is something like the Substance Painter add-ons which allow shifting of data. Even then, each bit of software has a unique addon which interprets the material.