Nice and smooth

Hello, I tweaked the UI of pronterface to fit a 3.5" LCD display nicely on a pi3, now I want to make a nice case for it. I was going to design one but on this link [www.thingiverse.com]., it already has a nice looking one designed and I downloaded all the necessary .stls.
My question is, how to make the surfaces so smooth like you can see in their pictures? Do they use PLA or ABS? What kind of post printing process is needed to polish the surface to be smooth? What settings it may be in creatieng the gcode? Thanks.

Edited 2 time(s). Last edit at 02/15/2018 07:39AM by rich1812.

Use a good renderer in your 3d model program like they did

Acetone vapor treatment works for ABS but not PLA. PLA sands better than ABS. High fill paints work well for smoothing prints.

They haven't done anything special to the prints in the pictures. If it looks smoother than normal, its because the pictures are low resolution and slightly out of focus.