Nudity - Underwear
Unless disabled in settings, every Sim has an additional layer of clothing that is underwear. Undressing top or bottom half of the Sim body will reveal their underwear. Sims with the 'No Underwear' trait will not wear underwear.
Underwear can be set per Sim and per every outfit that Sim has using the ‘Change Sim Underwear’ interaction when clicking on a Sim. That will open the Underwear Mannequin CAS Screen. Underwear cannot be removed from a Sim by using the Underwear Mannequin CAS Screen.
Sleepwear and Swimwear outfits don’t have underwear.
Underwear doesn’t have any additional functionality other than its visual aspect.
The ‘ww.random_sims_underwear’ command can be used to randomize underwear for all NPC Sims in the game.