Maybe its time for me to try to explain the mysteries of Sims "skins".
Dr. C has kindly given us much info about the Sims file structure. I'll
try to explain what he has revealed, along with what I have discovered.
Here goes:

The appearance of your Sims characters is determined by two files. A
mesh (or .skn) file defines the character's shape, and a texture (or
.bmp) file which applies the colors of the clothing onto the mesh.

============================MESH FILES================================

Lets look at a MESH file name first: xskin-b300faFIT_01-BODY.skn
We'll break it apart:

PREFIX: xskin
(It's a mesh file)

BODY TYPE: -b325faFIT_01-
(In between the dashes, this identifies the general body type. In this
case female adult fit & b325 - long dress)

INDIVIDUAL NAME: BODY
(This part of the name can be anything the creator of the mesh wants it
to be. It identifies this particular "b325" mesh, since there can me
many different b325 meshes.)

EXTENSION: .skn
(Windows file type identifier. However, since the Mac version is a
direct port the Mac version also looks at these.)

BTW renaming these files is not a trivial matter. I'll come back to this
issue later.

=============================TEXTURE FILES==============================

Now lets look at a corresponding TEXTURE file name: B325FAFitlgt_RedDress01.bmp


BODY LINK: B325FAFitlgt_
(This links this particular bmp file with the "B325 female adult fit
long dress " mesh. This graphic will only be shown on any b325FAFit long
dress body style if the character has light skin as determined by the
"lgt". med=medium skin and drk=dark skin)

INDIVIDUAL NAME: RedDress01
(Again this can be anything you want, but it is important to understand
that when this outfit is worn this is this name "RedDress01" that is
defined as the character's "normal clothes".

You can easlily rename these bmp files but you should NOT have more that
one bmp file with the same INDIVIDUAL NAME in your skins folder.

======================SPECIAL DEFAULT TEXTURE FILES ==========================

There are a few special bmp file names reserved for: pajamas, swimsuits,
nude, and formal. Lets take a close look at one of these:

Swimsuit: UFFitlgt_undies01.bmp

BODY LINK: UFFitlgt_
(U=underware/swimsuit F=Female Fit=fit lgt=light skin This bmp file is
linked as the swimsuit texture for fit light skinned females.)

INDIVIDUAL NAME: undies01
(01 or undies01 is a special name that tells the program that this is
the DEFAULT swimsuit bmp and should be applied to all light skinned fit
females _unless_ there is a custom swimsuit defined.)

Creating a custom swimsuit link is easy. A custom swimsuit is created by
linking a swimsuit bmp to a DAY OUTFIT. If I rename any swimsuit bmp to:

UFFitlgt_RedDress01.bmp

I have created that link. Now any character who wears "RedDress01" will
change into that swimsuit when swimming!

By now you should see the pattern. There are different body shapes (.skn
files). Day outfit textures can be linked to each body type. Different
swimsuit, pajama, nude, and formal textures can be link NOT to a body
type, BUT to specific daytime outfits. That way anytime you Sim changes
their daytime outfit, the swimsuit, pajamas, etc. that they wear would
change too!

All the other special (pajama, nude, & formal) file names follow the
same pattern (You will find a list of all of them at the end of this
explanation). Rename a bmp file to the special file name listed below to
make them the default texture, or change the INDIVIDUAL NAME part to
link the texture to a specific daytime outfit.

=========================CHANGING THE DEFAULT MESH (.SKN) FILES===================

Are you kidding!! ;-) That's enough for now. Stay tuned for Part Two

-Paul

============================SPECIAL RESERVED BMP FILE NAMES=======================
Adult Pajamas
PajamaFLgt_01.bmp
PajamaFMed_01.bmp
PajamaFDrk_01.bmp
PajamaMLgt_01.bmp
PajamaMMed_01.bmp
PajamaMDrk_01.bmp
Child Pajamas
PJsFLgt_01.bmp
PJsFMed_01.bmp
PJsFDrk_01.bmp
PJsMLgt_01.bmp
PJsMMed_01.bmp
PJsMDrk_01.bmp
Custom Pajamas
PajamaFLgt_customnamehere.bmp
PajamaFMed_customnamehere.bmp
PajamaFDrk_customnamehere.bmp
PajamaMLgt_customnamehere.bmp
PajamaMMed_customnamehere.bmp
PajamaMDrk_customnamehere.bmp
Adult Swimsuits
UFSknLgt_undies01.bmp
UFSknMed_undies01.bmp
UFSknDrk_undies01.bmp
UFFitLgt_undies01.bmp
UFFitMed_undies01.bmp
UFFitDrk_undies01.bmp
UFFatLgt_undies01.bmp
UFFatMed_undies01.bmp
UFFatDrk_undies01.bmp
UMSknLgt_undies01.bmp
UMSknMed_undies01.bmp
UMSknDrk_undies01.bmp
UMFitLgt_undies01.bmp
UMFitMed_undies01.bmp
UMFitDrk_undies01.bmp
UMFatLgt_undies01.bmp
UMFatMed_undies01.bmp
UMFatDrk_undies01.bmp
Child Swimsuits
UFChdLgt_undies01.bmp
UFChdMed_undies01.bmp
UFChdMed_undies01.bmp
UMChdLgt_undies01.bmp
UMChdMed_undies01.bmp
UMChdMed_undies01.bmp
Custom Swimsuits
UFFitLgt_customnamehere.bmp
UFFitMed_customnamehere.bmp
UFFitDrk_customnamehere.bmp
UMFitLgt_customnamehere.bmp
UMFitMed_customnamehere.bmp
UMFitDrk_customnamehere.bmp
Custom Nudes
NFFitLgt_customnamehere.bmp
NFFitMed_customnamehere.bmp
NFFitDrk_customnamehere.bmp
NMFitLgt_customnamehere.bmp
NMFitMed_customnamehere.bmp
NMFitDrk_customnamehere.bmp

*Custom swimsuits and nudes must be create BEFORE you create the
character. You cannot go and change them later.

-=Computer Controlled Characters=-

Postal Worker
Postalface.bmp
Postalhat.bmp
Postalsuit.bmp
Pizzaguy
Pizzaguyface.bmp
Pizzaguysuit.bmp
Pizzahat.bmp
Burglar
BurlgarMLgt_01.bmp
BurlgarFLgt_01.bmp
C_Burglar.bmp _GUAO_thief.bmp (hands)
Firefighter
FireFighterMFit_01.bmp
C_Firefighter.bmp
Repairman
HandyMFat_01.bmp
C_Handy.bmp
Police
PoliceFLgt_01.bmp
PoliceFMed_01.bmp
PoliceFDrk_01.bmp
PoliceMLgt_01.bmp
PoliceMMed_01.bmp
PoliceMDrk_01.bmp
C_Police.bmp
Repoman
RepoMFit_01.bmp
C_Repo.bmp
Gardener
GardenerFFat_01.bmp
C_Gardener.bmp
C_Gardenhat.bmp
Newspaper Girl
NewsieFChd_01.bmp
C_Newsie.bmp
C_Newshat.bmp
Maid
Maid.bmp
C_Maid.bmp
Social Worker
SocWkrFSkn_01.bmp
C_Socwkr.bmp

-=Career Paths=-
Buisness Suit
BusinessMLgt_01.bmp
BusinessMMed_01.bmp
BusinessMDrk_01.bmp
BusinessFLgt_01.bmp
BusinessFMed_01.bmp
BusinessFDrk_01.bmp
Paramedics
EMTMLgt_01.bmp
EMTMMed_01.bmp
EMTMDrk_01.bmp
EMTFLgt_01.bmp
EMTFMed_01.bmp
EMTFDrk_01.bmp
Ranger
RangerMMLgt_01.bmp
RangerMMed_01.bmp
RangerMDrk_01.bmp
RangerFLgt_01.bmp
RangerFMed_01.bmp
RangerFDrk_01.bmp
Mid-Scientist
SciMidFLgt_01.bmp
SciMidFMed_01.bmp
SciMidFDrk_01.bmp
SciMidMLgt_01.bmp
SciMidMMed_01.bmp
SciMidMDrk_01.bmp
Scientist
ScienceFLgt_01.bmp
ScienceFMed_01.bmp
ScienceFDrk_01.bmp
ScienceMLgt_01.bmp
ScienceMMed_01.bmp
ScienceMDrk_01.bmp
Doctor
ScrubsFLgt_01.bmp
ScrubsFMed_01.bmp
ScrubsFDrk_01.bmp
ScrubsMLgt_01.bmp
ScrubsMMed_01.bmp
ScrubsMDrk_01.bmp
Top Cop
TopCopFLgt_01.bmp
TopCopFMed_01.bmp
TopCopFDrk_01.bmp
TopCopMLgt_01.bmp
TopCopMMed_01.bmp
TopCopMDrk_01.bmp
Top Doctor
TopDocFLgt_01.bmp
TopDocFMed_01.bmp
TopDocFDrk_01.bmp
TopDocMLgt_01.bmp
TopDocMMed_01.bmp
TopDocMDrk_01.bmp
Mayor
MayorFLgt_01.bmp
MayorFMed_01.bmp
MayorFDrk_01.bmp
MayorMLgt_01.bmp
MayorMMed_01.bmp
MayorMDrk_01.bmp
Mobster
MobsterFLgt_01.bmp
MobsterFMed_01.bmp
MobsterFDrk_01.bmp
MobsterMLgt_01.bmp
MobsterMMed_01.bmp
MobsterMDrk_01.bmp
Politician
PoliticsFLgt_01.bmp
PoliticsFMed_01.bmp
PoliticsFDrk_01.bmp
PoliticsMLgt_01.bmp
PoliticsMMed_01.bmp
PoliticsMDrk_01.bmp
-=Misc=-
Wedding Outfits
FFSknLgt_01.bmp
FFSknMed_01.bmp
FFSknDrk_01.bmp
FFFitLgt_01.bmp
FFFitMed_01.bmp
FFFitDrk_01.bmp
FFFatLgt_01.bmp
FFFatMed_01.bmp
FFFatDrk_01.bmp
FMSknLgt_01.bmp
FMSknMed_01.bmp
FMSknDrk_01.bmp
FMFitLgt_01.bmp
FMFitMed_01.bmp
FMFitDrk_01.bmp
FMFatLgt_01.bmp
FMFatMed_01.bmp
FMFatDrk_01.bmp
GFAO_Bride.bmp (hands)
Military Cadet Child
MilCadetULgt_01.bmp
MilCadetUMed_01.bmp
MilCadetUDrk_01.bmp
Military Leader
MilitaryFLgt_01.bmp
MilitaryFMed_01.bmp
MilitaryFDrk_01.bmp
MilitaryMLgt_01.bmp
MilitaryMMed_01.bmp
MilitaryMDrk_01.bmp