http://willswing.com/news.asp?newsSeek=779

T2C Sailcloth Update As of the beginning of this year, all ODL06
sail material is now designated UVODL06, and uses the UV protected Mylar film.
This change is in effect for all T2C sails using ODL06 that were cut after
November 30th, 2011.

As a result of this change, we strongly recommend that UVX15T, rather than
PX15T, be used on the number one panel (leading edge) whenever UVODL06 is
selected for Panels 3 and 4 (top surface and trailing edge), otherwise the
number one panel would not be UV protected, and the service life of the sail
would be reduced unnecessarily.