There is normal Q power that is quite thick compared to most other kite lines, and Q power pro, which is 30% smaller and comparable with more standard line sets. The diameter seems to matter less to over all drag compared to the frequency that the lines oscillate at while flying. Q power is perfectly round in cross section so it oscillates at a much higher frequency than kite line that is more squared or flat cross section. The amplitude of the sin wave that it cuts through the air is smaller despite its larger cross section. The higher frequency of Q power line is actually audible while flying. It sounds a bit like a tie fighter! The lower frequency at which most kite lines oscillate is not audible.
This is taken directly from their site:
"Round cross-section helps minimize ribboning effect. - What is ribboning effect?
- The tendency for normal hollow braided Spectra line to flatten and then act like a ribbon in the air, vibrating back and forth. Thereby having a much greater effective drag than the apparent static diameter would suggest.
Q-POWER LINE’s internal core bundle of fibers resists the tendency to flatten out and when compared to traditional braided line Q-POWER LINE has a very round cross-section. This round cross-section minimizes the effective diameter and drag. Traditional braided line can have an effective diameter of up to 5X the lines static diameter, substantially increasing parasitic drag."
There is a data sheet on their site, but it doesn't mention line diameter.... It also seems to have type setting issues!