Hi Arthur,
The STL output is just the same triangles as in the ChimeraX surface(s).  I believe many users use separate software for triangle decimation after doing the export, but there also some surface parameter settings in ChimeraX you can adjust before exporting to see if that helps.

Please see these previous posts for details on adjusting the surface triangles in ChimeraX:

<https://mail.cgl.ucsf.edu/mailman/archives/list/chimerax-users@cgl.ucsf.edu/message/SPPOD2B6E7ESWROWPA6ED6EWDNTUVGR7/>

I hope this helps,
Elaine
-----
Elaine C. Meng, Ph.D.                       
UCSF Chimera(X) team
Department of Pharmaceutical Chemistry
University of California, San Francisco

> On Sep 25, 2023, at 9:56 AM, Arthur Melo via ChimeraX-users <chimerax-users@cgl.ucsf.edu> wrote:
>
> Dear colleagues,
>
> Is there a way to refine or decimate a mesh of a map to save as an STL file?
>
> All the best,
> Arthur