I have recently created a hairstyle from scratch in 3DStudio Max. I exported an .obj in that program and put it into Milkshape, where the mesh looked fine. I followed all steps of the hair tutorial and managed to get the mesh in game, where it works fine except for one thing. There are triangles all over the hair:




The hair works fine in game, I can use it in live mode, I can zoom in and out with reckless abandon, it shows up fine on the sim thumbnail - aside from the triangles of course. I had thought originally that the underside of the hair was poking through the mesh, so I rebuilt the underside and triple checked and still no dice. Even in places where I have completely deleted the undersides as it doesn't need to be there are the weird triangles (for example, the top of the head). As my screenshot shows, it looks normal in Milkshape. Does this mean it is not a problem with the mesh, but with the textures? I haven't seen this issue anywhere before so I'm wondering if there was a problem with my exporting it from 3DS Max.

Any ideas on how to fix this would be greatly appreciated.

Those are reverted faces.
Open the mesh in Milkshape and select just one hairlayer, right click in the 3d view window and untick the option
''draw backfaces''
If you see the same in milkshape as on the screenshot you have a big problem, you have to reverse those faces by selecting them and reverse them back.

I just realised sims 3 hairmeshes dont have the seperate layers visible in milkshape so you can not select the inside or outside of the hair as seperate layer....maybe turning autosmooth on will show the reversed faces(you will need to edit before autosmooth starts working, mirror and mirror back for instance)

i have seen this problem alot on free to download meshes on 3d model sites....

Here's what the hair looks like in Milkshape with backfaces turned off in both smooth shaded and flat shaded modes:



If the normals were flipped, there would be holes, right? I'm not sure how it works in Milkshape and I don't know if there's a way in Milkshape to actually check the normal direction but with backfaces off it doesn't look like there are any errant normals. I tried turning on Auto Smooth and moving some verts to see if that would show any abnormalities but it still looks the same. I'm going to try pressing this "Smooth All" button and seeing if that makes any difference.
edit: Nope, Smooth All didn't do anything.

The problem with the faces is that both faces are reversed, the ones from the outside layer are reversed but the ones from the layer underneath(for the inside textures) is also reversed, thats why it is so hard to locate them as one covers the other.
With sims 2 you could hide the inside layer as those were seperate groups, you cant with sims 3.

If you really want to fix this you have to first seperate the out and inside layers.
You will need to use the function ''ignore backfaces'' on and select and seperate all layers used in the mesh.(this can be a alot of work...)
When you then turn off ''show backfaces'' you will see the holes of the faces that are reverted.

I am not 100% sure but it is even possible you need to remap the hairlayers on the uvmap when done.

You say you have made this hair from scratch? Then you must have a backup when the layers were seperated?
Fix that one and then copy the outside layer again for the inside textures.

I have not made hairmeshes for sims 3 but i think you must have both(or more) layers first seperated in Milkshape as you also need to fix the opacity with Wes H his extra data tool before you can regroup the layers into one.
You have not done this either as the inside textures in the neck area overule the front hair textures(darker area on the CAS screenshot)

Here is an older file without the undersides, backfaces off, in flat shaded mode:



As you can see there doesn't appear to be any normals facing in the wrong direction. No holes in the mesh.
The pieces of hair that come out around the neck are also intentional, they are mapped in such a way that they can be a different color as to give the illusion of having the underside of the hair dyed (as mine is, it was for a self sim). The extra data tool was in fact used and the actual inside of the hair is darker than the outside.
Anyway, I have double and triple checked my normals in three different programs and I cannot see any holes or flipped normals in any of them. I'm going to try exporting the hair without undersides into the game to see if this still appears.

I had a mesh I made like this once. The edges were not smoothly aligned.

I spent a lot of time trying to adjust the normals, but in the end I had to move the vertices along a curve to get them all aligned.

Thanks Wes, I'll try moving around the verts in the mesh manually then and seeing if I can get better results. Seems like a time consuming process but if it works I'll be a happy cat.

Another thing causing it also can be duplicate faces but you prolly checked that out.
srry i was wrong bout the reversed faces...i could have swear.

Thanks for trying to help me out Base, I really appreciated your input. WesH was right, the mesh itself just needed some verts moved around so I hit the relax tool a few times in 3DS Max and it solved most of the major trouble spots. I'll keep working to refine it and hopefully it'll be pretty enough to share eventually. Thank you both!