Hi Matt, First, Chimera VRML rendering of transparent objects is wrong and generally not useful. It simply adds the brightness of all overlying surface layers. Correct behavior dims the appearance of layers in back because they are viewed through the layers in front. The wrong behavior gives no cues as to what is in front or in back and results in saturated full intensity colors when surfaces are more opaque than transparent. The Chimera implementation is just a cheap approximation to correct transparency. The code would have to be much more complex to draw the transparency correctly. Given that Chimera ignores the depth of VRML surface layers I'm surprised it renders slowly. How does the rendering speed of the original volume data in Chimera compare? I would expect that to be slower because it actually resorts the surface triangles by depth each time they are drawn. You can check exact frame rates using the Chimera benchmark tool, menu entry Tools / Utilities / Benchmark. I have plans to optimize the rendering of transparent volume surfaces -- I think it could be nearly as fast as opaque surfaces with some fancier code. It is unlikely we will make our VRML drawing handle transparency correctly since VRML viewing is not a primary function of Chimera. It might be possible to change the VRML implementation to use our volume / molecule surface code but many other Chimera projects have higher priority. Tom