pex for hot water radiator heating
The tubing for radiators incorporates a special oxygen shield to keep the oxygen from the air out of the tubing, otherwise the oxygen reacts with iron in the water to form iron oxide (rust). Normal PEX tubing used for potable water does not have the oxygen barrier, so it is not suitable for radiator use. The color of the tubing does not tell you anything, you need to check the writing on the tubing to make sure it is oxygen barrier PEX. If it does not say explicitly that it is oxygen barrier PEX, the tubing may have a manufacturer identification mark on it that can be traced to the manufacturer's website, where hopefully it will state whether it is oxygen barrier PEX or not.