Hey this has probably been answered somewhere but I couldn't find it.

I'm working in UDK more extensively and I have models that have their UV's split right down the middle.

I flip the UV's and stack them. When I import it into UDK I get a nasty seam from the normals where the two mirrored sides meet.

I heard there is a material that fixes this in UDK but I wasn't sure what it was...

Thanks

Make sure your seams run vertically like the pages of a book not the pages of a calendar. Any other direction will cause a visible seam. Even then it's not perfect. It also has a bit to do with how you layout your lightmap UVs.

Read more about the issue from this thread.

EDIT:

After using lightmass to bake lighting for a bit now I'd say sometimes it helps to not split mirrored lightmap UVs, but to merge them instead.

Oh wow, thank you so much Ben! That worked like a charm. At first I thought it didn't but after deleting and reimporting the object again it finaly updated and no seams! Thanks again!