There are A LOT of fakes out there. they claim to be 4 gauge and the outer jacket of the wire will be almost a quarter inch thick and your barely getting an 8 gauge wire. I used
KnuKonceptz Kolossus 4 Gauge and i was very happy with it. It truly is a 4 gauge wire but is very pliable and easy to route plus the cost is awesome compared to the other way overpriced name brands (kicker, monster etc)
here is an example of "wanna be" cheap 4 gauge the blue is KnuKonceptz
http://www.knukonceptz.com/Images/wirecloseup.JPG