(Meshlab) How to fix: Mesh smoothing not saving in .stl file

Question

I have been trying Meshlab software for smoothing an .stl. I used Butterfly smoothing filter and tried others just to be certain. After applying the smoothing filter, it worked nicely. Then I exported the file and saved it. However, when I open the saved file afterwards it goes back to the original un-smoothed version, each time (when I open it on meshlab, meshmixer, chitubox). Same problem persists even if I export the mesh as another type of file (.obj). Looking around for similar questions people suggested using the Freeze Matrix command but not even this worked. Does anyone knows how to fix this?

Answer 1

STL file format does not support multiple normals per triangle (smoothing), therefore you can only get plain triangles from it.

OBJ file format supports smoothing instead, I'm surprised to hear that you are unable to write a triangle mesh with smoothing using this file format.