Цитата из LightWave 6.5 AddEnum :
"Because volumetrics are ray-traced, to see a hypervoxel behind a transparent surface, you must force refraction. This means thetransparent surface’s Refraction Index (Surface Editor) must be greater than 1.0 (even 1.001 will work). You must also have Ray Trace Refraction enabled on the Render Options panel."