I've always used the terms interchangably also.
Today I decided to google "dyneema vs spectra", the most detailed answer I found was here:
http://en.wikipedia.org/wiki/Ultra_h...t_polyethylene
Bottom line is:
"
Trade names
Dyneema is a registered trademark of Royal DSM (The Netherlands). Dyneema was invented by DSM in 1979. It has been in commercial production since 1990 at a plant in Heerlen, the Netherlands. In East Asia, DSM has a cooperation agreement with Toyobo for commercial production in Japan. In the United States, DSM has a production facility in Greenville, North Carolina, which is the largest production facility in the United States for UHMWPE fiber.[4]
Honeywell developed a product identical in chemical structure, which is sold under the brand name Spectra. Though the production details are somewhat different, the resulting materials are comparable in properties.[5]
Other trade names for powdered or consolidated UHMWPE materials include TIVAR by Quadrant EPP, Polystone-M by Röchling Engineering Plastics, Tensylon by Integrated Textile Systems, GARDUR by Garland Manufacturing, GUR by Ticona, and UTEC by Braskem."
As far as sizing, here's all I could find on Cabrinha lines... as an example:
"Cabrinha Kite Lines
Sewn ends with polyethylene covering to protect the stitching. These lines are prestretched and sewn to an exact length. At a .04 inch diameter these lines will reduce line drag and get you upwind faster.
Sold in pairs.
Available in several line lengths:
17.5 meters
19 meters
22.5 meters"