If you create Sims skins, sooner or later you will probably want to use b300 meshes. These are the meshes commonly used for nude, underwear, and swimwear skins, as well as any outfits that are skin-tight.

These meshes are all made by Maxis. Each zip contains the skn and cmx file (no bmp files, though).

• b300fafit: female adult, fit
• b300fafat: female adult, fat
• b300faskn: female adult, skinny
• b300mafit: male adult, fit
• b300mafat: male adult, fat
• b300maskn: male adult, skinny
• b300fcchd: female child
• b300mcchd: male child

Since these are Maxis meshes, I'm pretty sure you can alter or distribute them however you like.