I’m struggling with this issue. I just want to extrude this open polysurface to get thickness. No matter what I extrude them, it is extruded individually. (Guess it’s because it is not surface) Any way to convert it to one single surface ?
Simple workaround (assuming no internal gaps in the polysurface): DupBorder the polysurface. ExtrudeCrv the duplicated border by the desired thickness. Copy the polysurface to the edge of the extuded border. Join the original polysurface, the extruded border and the copied polysurface.
A similar proceedure should be possible in Grasshopper.