In the last few years hang glider manufacturers have offered
topless gliders with see through/clear sails led by the example from Wills Wing
(at least it appears that way to me). These gliders use laminated sailcloth with
black Technora threads. Wills Wing offers two laminates: UVODL06 and UVODL04,
both with UV films. Wills Wing writes:

Technora is three times stronger than polyester fiber.

Carbon reinforcing tape is used with UVODL04 to provide additional strength and
resistance to stretch along the major tension lines. UVODL04 is slightly less
expensive than UVODL06 but the cost and application of carbon tape make the
UVODL04 sail more expensive. Generally results in lighter, quicker handling.
Available only on the T2C.

http://www.teijinaramid.com/aramids/technora/technora-filament-yarn-black/

Steve Pearson writes about these laminates:

UVODL04 is 135 grams/m^2 or 3.2 oz./sailmaker's yard (36 in x 28.5
inches) . That includes two layers of 0.75 mil film, 400d Technora scim, 750d
Technora X-ply, and adhesive.

UV ODL06 is 165 grams/m^2 or 3.9 oz./sailmaker's yard. That includes two layers
of 0.75 mil film, 750d Technora scim, 750d Technora X-ply, and adhesive. Heavier
scrim yarns make it harder to see though.

The clear appearance is the natural condition of polyester film when used with a
clear adhesive. If one used a colored adhesive, it would be opaque like our UVPT
white and UVX15 (http://willswing.com/features/sailcloth.asp).
If I used grey film, like UVPT grey, it would be somewhat translucent, but not
as clear.

The other reason that lightweight Technora laminates are clear is that you need
much less Technora fiber (smaller, denser yarns) to achieve the required
structural design parameters. The sparse fiber matrix leaves more clear film
exposed.

Technora sails have become quite popular despite the fact that
they are more expensive. Is it the bling factor or how the gliders handle or
both?

The Wills Wing T2C:

UVODL04 with UVODL06 leading edge. Notice the additional lines/threads of
Technora.

The Icaro 2000 Laminar:

The AIR VR:

The Aero Combat:

The Moyes Litespeed:

The Moyes Litespeed is the latest glider to use the clear Technora laminate. The
Litespeed is the only glider not to have the clear Technora laminate go all the
way to the trailing edge. It is not clear from the Moyes web site what sailcloth
is used for the trailing edge.

I am only able to find detailed descriptions of sailcloth material at the Wills
Wing web site. I don't find any other hang gliding manufacturer providing this
level of information about the sailcloth that they use. If I could find such
information I wouldn't have to rely so heavily on the Wills Wing site. If you
have a link to such information I would be happy to publish it.

I don't even have a detailed description of the other Technora laminates used by
other hang glider manufacturers. Even the sailcloth manufacturer web sites are
bereft of useful information.

http://willswing.com/features/sailcloth.asp.

A key issue is that UVODL06 and UVODL04 require a special order and a minimum
order, unlike ODL04 and ODL06. In addition, UVODL04 and UVODL06 are a bit
more expensive. The minimum order is 1000 meters. Perhaps this is another area
where hang glider manufacturers could agree to a joint purchase, now that this
material is so popular.