SinisterControls Didn't mean to ruffle your feathers. I do respect your knowledge.
Polyethylene is $9 for 100 foot roll making it cheaper, but it's not only the cost savings. It's also better because it has a smaller inside diameter and lets the air flow better. It also releases easier from the fittings (when you want it to). Polyurethane certainly has some advantages (such being more durable and flexible then polyethylene). But my point was that for our industry polyethylene is the airline of choice.
As to worrying about the "hardness rating" my point was that is just adding an unnecessary level of complexity to the conversation which only serves to confuse people. One of my missions is to educate people as to how easy it is to get into this stuff. I was trying to point out that having to know that piece of information is unnecessary.