http://ozreport.com/forum/viewtopic.php?t=20682

Wills Wing and designer Steve Pearson have been staying on the
innovative edge of sail fabrics. I recently blogged about how the Technora
topped T2's look and are holding up.

Further explanation of PE or
PEN fabric from Steve Pearson: PE - (or PEN fabric) is similar in construction
to the PX styles except that the rectangular scrim and diagonal X-ply fibers are
higher strength and stiffer than polyester which improves both handing and
performance. We offer the PEN fabric in two styles which are structurally
identical except for UV resistance. The grey-smoke color uses standard PET
(Mylar) film. The bright white material uses clear UV film with bright white
adhesive (often referred to as titanium dioxide coating) between the film and
the underlying fibers. UV film is not a coating, but a PET film that is
molecularly altered for superior UV stability. In general, UV coatings between
the film and underlying fibers (like titanium dioxide) offer very little benefit
for the longevity of laminated sailcloth.

Check out the link above for more pictures and explanation.