(I promise this link isn’t a snuff film, though it does have some cartoon violence.)
A mod should certainly restore the link in the OP, which is interesting and not a problem in any way.
As for the question, Chronos is correct: a surface that binds tightly to air molecules has limited potential to increase drag.
It may be worth noting that a technique of increasing surface area has potential to reduce drag. Ridges aligned with fluid flow have been shown to do this. Shark skin embodies this effect, and it has apparently been studied in bats.
Google “riblets” for further info.
Your very large cape doesn’t even need special materials; it just needs to be very large.
An extremely large flag on an extremely windy day can produce enough aero drag to seriously stress the flagpole upon which it’s flying. Just increase the size of the flag until it produces enough drag to bear the weight of itself and a passenger at some reasonable descent speed, say 300 feet per minute (3.5 MPH).