Oxygen barrier has an interior coating of EVOH (ethylene vinyl alcohol) polymer which is less oxygen-permeable than the polyethylene of the tubing.

So can you explain it to me a little more thoroughly, I have read about the EVOH, but i do not understand what is the point for it.

So your saying oxygen permeation will corrode the system from the inside? How is that possible? Where will the oxygen even enter the tubing in the first place?

It goes through the plastic - that's what permeable means.

The oxygen enters through the plastic? That's hard to believe. If oxygen enters through the plastic doesn't it mean the connection wasn't secure?

Look up the term permeable. It's a basic scientific concept.

Just because water can't pass through the plastic, doesn't mean that air can't. It's impermeable to water, but permeable to gases. Water molecules are bigger than oxygen molecules.

Ever wonder why balloons deflate when they've been sitting around for a while? It's because the plastic that makes up the balloon allows the air to pass through it (albeit very slowly).

I've never let a water balloon sit around too long, so I'm not sure if they're impermeable to water. Maybe the water would seep through slowly too. Or maybe not.

But I think it's safe to say that if you filled a balloon with sand it wouldn't seep through. The balloon is impermeable to sand.

It has nothing to do with the connections. You think of the plastic as 'solid', but that doesn't mean that stuff can't pass right through it.

Same way that water resistive barriers are not vapor barriers. They stop water but allow the product it is protecting to dry out at the same time.

Oxygen molecules are smaller than water molecules and are able to go through tiny gaps between polymer chains. Your ability to believe it is not required in order for it to be true. If this is not you attempting some sort of bizarre joke, just google how oxygen barriers work. Good grief.

Installing the wrong type of PEX may catastrophic for your system use this link http://www.canarsee.com/differences-between-oxygen-barrier-and-non-barrier-pex-tubing best source what i found on the internet.

Bad analogy, but think of a sponge. When you look at a sponge, you can't see through it. To a certain extent it looks solid. But you know that the sponge is porous, that things can pass through it. Some things are too large to pass through the porous structure of the sponge. Some things are small enough to pass through the sponge.

Same with PEX. PEX looks solid. For all intents and purposes, it IS a solid. It holds liquid water. But things can still pass through it. Oxygen is one of those things.

Water has dissolved gases in it, oxygen being one of them. In something like a closed heating system with a cast iron boiler, oxygen can be a bad thing. Oxygen plus cast iron? Not a good combination. Iron plus oxygen? Rust. You don't want to rust out your cast iron boiler.

In new installation, dissolved gasses in the system will eventually work their way out of solution and be purged from the system, especially if the water is heated. If you have PEX in this system, say with radiant floor heat? If your PEX does not have the O2 barrier, then atmospheric oxygen can pass through the wall of the PEX and enter your closed water system. The circulating water will then carry the oxygen to your cast iron boiler, potentially causing damage to your cast iron boiler.

The oxygen barrier in the PEX prevents additional oxygen from getting into your closed system, so once the initial dissolved gasses in the water come out of solution and are purged after system start-up, you have "dead water" in your heating system. "Dead water" will not rust your cast iron boiler as there is no free oxygen in the water to react with the iron in the boiler.

Hope that makes sense.

Thanks alot guys and girls, between what I've read on the internet, on this forum, and what jordan hvac stated I think i got a good grasp on the topic.

The EVOH Coating is on the outside!!!