I have a glTF model from Blender which is displaying unwanted transparency. I originally duplicated the model and flipped it over to create the whole thing. The duplicated half is showing the transparency. I’ve attached a screenshot from Sandbox.
I tried switching off backface culling which made the duplicated side opaque but gave it a completely different colour.
Seems like it could be normals issue, not transparency. Try turning off backface culling to be sure you have the right problem.
Ahh, did not see you did the culling test at the bottom of your post. Looks like you have both problems. I do not do / use that exporter. You can probably fix it on the BJS side by changing the material, if that is acceptable till anyone who knows something about gltf coming from Blender:
material.transparencyMode = BABYLON.PBRMaterial.PBRMATERIAL_OPAQUE;
Thanks for the help @JCPalmer, the main problem was normals on the model, flipped round fixed the problem 
I’ve got something weird going on now. In my extended model I have a hover state which is supposed to be just a green outline. But since adding mat.needDepthPrePass = true the model turns black on hover as well as the green outline.
