SlickLine is a brand name; I think it is polypropylene. It does have a bit of a 'memory', i.e. kinks tend to form where knots were tied, but that's a minimal problem to me.
It's a much thicker line than ZingIt and that's one reason I like it.
Wesspur carries 'Slick Line', but this doesn't look like my SlickLine, but maybe it's an 'improved' version???
http://www.wesspur.com/Throw-line/zing-it-throw-line.html
It's similar to Target Line, but Target Line seems awfully stretchy to me.
Interesting, I find it as easy to throw as the smaller lines and much easier to handle. But, true, it doesn't pack up as tight, but then the upside to that is it doesn't tangle as easily either.
Let me qualify that just a bit - I'm usually not throwing real high with any line. If it's over 30', I shoot it, and Slick Line may not shoot quite as far as some of the smaller lines, but that's not as significant to me as it would be others.