Dear hebeldebel,rnrn Currently, OpenLB supports STL-files as input, which indeed do not support material no. for different properties. A solution would be to read a set of STL-files and assign the material in the code. Some years ago, we had a Nastran interface but removed it since it is a valume based mesh which limits the executable size to the memory size. Recently, we introduced “”indicator functors”” for simple geometries like cones, sheres, cubes, .. as well as STLs. You can join, substract and intersect them like you do with set (cf. venturi3d example). We also do have an interface to the xml format, which makes it easy to write reades for other formats like DBS. I do see your point that it would be much easier to use another CAD-based program to set up the geometry. If you are interested in helping us to improve OpenLB in that direction, please contact me, using the contact forum.rnrnBestrnMathias rn