I bought 50' of 5/8" copper tubing CHEAP, when Home Depot was clearing out their old stock. $27.00, and OBTW, trying to make 5/8" bend in a nice circle was a bitc*. Since I got turned around during the winding, what should have been a nice rib cage turned into an Oh, Sh*t moment. I fixed it though, I have a 45' dual pass IC. The coolant goes through the tubing through both coils at the same time, as opposed to 25' and then 25'. It is like putting 2 ice cubes in a glass together, as opposed to one at a time, if that makes sense.
EDIT:
There are a few of us that have " finally" figured an easier way to coil an IC with little to no kinking: start at the middle of the roll when winding, if not, it is a real bitc* because when you get towards the middle, you have a tight coil to try to open and a short handle. When you start in the middle, you have a lot of leverage, due to the length and larger diameter of the remaining tubing. Trust me, don't ask.