Here's a thread from Bladeforums "gadgets and gear" section:

http://www.bladeforums.com/forums/showthread.php/731204-cool-paracord-project?hi...

I think you can view this without signing up, but the forum is full of good information and there are a number of whip-related threads.

Whips? 
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Just to make the conversation lowbrow

flat parachute cord works well, if you can find it. I use it for just about any braiding project I have. It only costs about 7-10 cents a foot.

I've never tried parachute cord before but if the core of the whip is heavy enough, they work ok.  Paul Nolan makes a great one.  They are cheap and durable, and popular in Florida where the humidity isn't good for leather. 

For a proper whip which handles correctly for fast work with multiple cracking, they are almost invariably made of kanagroo leather.  It's an incredible material, unique the world over.  It allows for dense hefty tight work which can be kept small in cross section and slice through the air with speed.  A good Australian whip can weigh less than a pound and be efficient enough to outperform many American bullwhips weighing over twice that or more.  They are expensive compared to the American whips, so keeping them out of the dirt is a good idea.  Yet if made right the maneuvers that can be done with them are mind blowing. 

Despite always being known as Whipartist, I've never posted any of my work on here before.  Here's one of the bullwhips I've made.  It's 24 plait at the butt and 8 plait at the point.