The title isn't an oxymoron....
I recently discovered (on my bathroom counter) a dental floss made from a fiber (fibre) from W.L. Gore (of Gore-Tex fame) that is some sort of continous synthetic fiber (i.e. no rough spots and/or shredding) and comes convienently wound on small spools coated with a very fine layer of "natural" wax. I can't break this stuff by hand. Seems significantly stronger than normal floss (which isn't that weak either) and is very uniform.
I've added a 50M spool to all of my kits!
They have a web site:
Glide Floss Web Site