@JoshKitney if after the settings above you are still getting black windows, the reason is because it is double sided, so you will want to experiment Max. Refraction Rays with higher values, but the best would be if the mesh wasn’t double sided, because I am not sure how the light bounces are being dealt in that such small area… it might be black because it is reflecting the car interior and the bounces are not enough to get through the windows. Refraction Rays increase will cost, so if you are looking for cinematic it is ok.