Keep your controller pristine and get a competitive edge with these flexible thumbstick covers for the 8BitDo SN30 Pro+ controller.
There are several different designs for customization. My favorite is "ThumbstickCover_Grippy_Beefgrip.stl" and, of course, the "_Clown.stl"
These are generally designed for flexible filaments, but there are also "_NonFlex" versions of several designs made for PLA or other stiffer materials... Really though, the softer and grippier the material the better. Ninjaflex TPU works pretty well.
If you like this, you may also be interested in my SN30+ Custom Faceplates