I've watched this issue for a long time but it seems this hasn't been fixed yet. My use case is to assign a UIView to the 'contents' variable of SCNMaterialProperty. It works without problem in terms of rendering, but when I assign 'nil' to the variable the allocated memory of IOSurface by SceneKit does not being destroyed I've searched about this and many other developers have been suffered by this issue. I did a 'Game Memory' profiling of my toy example and the allocated memory (134MB) by SceneKit hadn't been released after I've assigned nil. I'm sure I released every relavant UIViews and view controllers used for the 'contents'.