Crosslinked Polyethylene, also known as PEX, is a flexible tubing for hot and cold water distribution applications. PEX tubing is frequently used in both domestic water and in radiant heating applications. But not all PEX tubing is created equal. Domestic water systems can use normal (non-oxygen-barrier) tubing, because all metal parts of this systems contain non-ferris materials. So they don't rust - oxidize. This however is not the case for radiant heating systems. Pumps, boilers and valves used in these applications commonly have ferris components and therefore will oxidize and distribute residue throughout the system. This oxidation will also degrade the ferris components. For this reason oxygen - barier and aluminum core tubing is used in radiant heating applications..