Question about tubing

Ok so I need a little extra tubing for my cooling system. Now I just want to the hardware store and bought some, which is the same thickness (Both ID and OD) of the stuff that came with my kit. The tubing that case with my kit says that it is UV Tubing, while the tubing I got at the hardware store says it is Vinly Tubing.

What's the difference between the two?

Vinyl tubing is pretty useless for watercooling. It kinks readily and deforms when heated. It's only meant for fountain and aquarium use (relatively cold water applications where kinking doesn't matter).

You need PVC tubing, optimal brands being Masterkleer or Tygon. For a 1/2" loop you can use [1/2" ID 3/4" OD] tubing. Or you can use [7/16" ID 5/8" OD] tubing provided you dip it in hot water before pushing it over your barbs.
You can get the widest selection of tubing through http://www.mcmaster.com
For common sizes try
http://www.jab-tech.com or http://www.petrastechshop.com

So i have 1/2" id 5/8" od tygon tubing, i should dip it hot water then push it over the barbs? What exactly does that do, Expand the tubing then when it cools off it has a tighter fit around the barbs or what?

1/2" ID, 5/8" OD is 1/16" walled tubing. You'll get more kinks than you'd get with 1/8" walled tubing (Tygon or other), but it should fit on the barbs fine without heating (boiling). If, however, you find that it's kinking when you're making bends with it, then by all means, boil it and then use extra clamps to keep it round when you make the bend. Tygon molds very well so if you get it into the correct shape after boiling it, it'll stay in that shape after it cools down--the water in the cooling system isn't hot enough to cause it to loose the shape you put it in.

Edit: I didn't answer your original question. Boiling the tubing allows it to stretch more (or more easily) than it would otherwise. So, if you're putting 7/16" ID tubing on a 1/2" (8/16") barb having the tubing stretch easier is beneficial. When you're using 1/2" ID tubing on a 1/2" barb it isn't necessary.

I must disagree with the Cptn on the vinyl tubing. While he is correct that there are better options out there, I have used the stuff in several watercooling setups without problems. Kinking is the major difficulty, but can be overcome with the Swiftech tube wrapping thingys (that's a technical term ) or the judicious use of hose clamps in areas where kinking is a problem.

Of course, he is much more knowlegable than I, so you probably want to listen to him rather than me.

Tygon the way to go for sure....... If your in the US Home Depot carries the thick wall Tygon.......