PE RT Tubing
PE RT (Poly-Ethylene Raised-Temperature) tubing is the recommended method of plumbing your hydronic heating system. It is specially designed to withstand higher temperatures of water, as well as be quite flexible.
Additionally, it has a 5-layer design, with an Oxygen-barrier which protects against Oxygen leaking into the system. Oxygenated water over a long period of time causes corrosion.
It is available in 5 sizes, 3/8", 1/2", 5/8", 3/4" and 1".