I use the yellow gas tubing, mainly because it is more convenient. I searched all the hardware stores in my area for the other tubing, and none of them carried it. Aqua-flow is about 1 mile from my house and they give me a really good deal if I buy 500ft rolls.

The main difference I have noticed is that the gas tubing is quite a bit heavier. Also, the black tubing is supposed to be cheaper by the foot. At least that is what a friend of mine who switched from the gas to the irrigation tubing told me.

the yellow tubing is about 200 psi. 3/4" of the black tubing. I have some women who love it and others that like the liighter stuff. I figured out how Bodyhoops makes their collapsible hoop and think the yellow may be sturdier for how they do it.

gas tubing is heavier (more dense), stiffer, and holds its form better. however, it is also more expensive than irrigation tubing--and the biggest problem with gas tubing is the lack of good connectors for it.

with black irrig. tubing, you can use an "insert fitting connector", which is very convenient b/c you simply heat the ends of the tubing with a blowdryer and, Voila!, you insert the coupling for an easy and durable connection.

gastubing, however, usually involved metal inner fittings ($$$$$) which do not seem to form as permanent of a join. and you cannot use the other (irrig.) connectors with gas tubing b/c of differences in the INNER diameter of the tubings.

my verdict: tho i love the heavyness of gas tubing, irri. tubing is more cheap, convenient, durable, and versatile. gas tubing hoops that i have made have given some problems (with connections) in the long run.
if you are serious about making gas tube hoops, find a person who works with and connects that tubing as part of his/her job, and pick that person's brain for solutions to the connector problem. if you get any good advice, be sure and report back to us! :)