This is the tubing used to connect Blumat components to your water source. It's an 8 mm European style. You can also use US-style 5/16" drip tube but it's hard to find, not very flexible, and the fittings are harder to put in.
This white color version is good for keeping the temperatures down - better for nutrients and preventing a kind of "vapor lock" that can occur in some hydroponic systems.
Buying these larger rolls saves about 15%.
Dip tubing into hot water to make it easier when connecting / disconnecting fittings.