Hi,
I’m modeling a car, and I am wondering whether the windows should have a thickness to them in order for raytraced refraction to work properly? In other words, like real windows that have a depth to them, not just a 2-dimensional shape… Am I making myself clear? 
Thanks.
Roofoo
yes, you will need to make thick glass
Well, I dunno… you can paint interiors if need be. You can put a tinted surface with specular reflection. It’s all a matter of what makes the scene work. There’s a lot of ways to “cheat” a scene and save yourself some work, but if it’s gonna be important for me, the viewer, to look into that car and to see something important that you’ve put there, you’ve got two choices: - create appropriately believable (thick…) glass with a suitable amount of refraction; or … - cheat by rolling the window down. 
Either one of these approaches would work!
Hi!
I’m currently modelling a car too!
The outside is complete but I am not inclined to model the interior at the moment. Solution: I am making the windows 100% reflective. You see cars like that in hot countries and if you get the lighting right it can look good.
Why don’t you try that?
Thanks for all the replies! Ok, I guess I will go ahead and model thick glass, because I’m wanting to create a fairly realistic environment, and I don’t mind the extra work to get it to look really good. I was going to model an interior anyway, at least the parts you can see behind the windows… Anyway, car windshields usually aren’t tinted so that the driver can see out, but I may have some slight tint on the other windows, it depends on how it looks
Edit Ok, I found an answer to my question on the Blender 3D site…
http://www.blender.org/docs/2.32_release/release232_render.html
“- For correct refraction calculus, 3D models MUST have normals pointing in the right direction (consistently pointing outside). That way, refraction can ‘detect’ the thickness of a transparent material, whether it enters or leaves it. So, model for realistic glass always both sides of a surface.”