http://willswing.com/blogs/PilotBlogs/tabid/38/BlogID/5/Default.aspx

There are several distinct attributes associated with every fabric
style and I think it’s important to consider them independently in order to make
the choice that best suits your needs.

Appearance and fashion

Structural performance (strength, stiffness and weight)

UV stability and longevity

Flight characteristics

Price

Appearance and fashion often drive the marketplace. Pilots seem to let those
factors dominate the conversation simply because it’s easier to choose ‘what
looks good” when they don’t have easy access to technical details.

As an example of why choosing by ‘what looks good’ is a bad idea, consider that
white and black polyester fibers look just like the much stronger Technora and
PEN fibers. Similarly, UV-modified film is indistinguishable from clear
polyester film but lasts more than twice as long in strong UV environments. So,
not only can’t you tell from inspection how well a fabric will perform, but it
often takes 100 or more hours of airtime for a superior fabric to show its
advantage.

We introduced fabrics based on high-strength PEN and Technora fiber over a year
ago. High strength and stiffness are essential to control twist and prevent
trailing edge flutter especially as gliders age. PEN and Technora fabrics offer
significant advantages over the popular ‘PX’ polyester-based styles. Our
PEN-based fabrics weigh 180 gms/m^2, match the structural performance of PX15T
(270 gms/m^2) and exceed the common PX10T style (230 gm/m^2) typically used on
trailing edge panels. ODL Technora-based fabrics are even stronger with a 20%
weight savings compared to PEN.

The article continues on at length
here.