I think op may be referring to 'barrier pipe', which is a plastic -copper-plastic sandwich, which is designed to keep out pollutants which can diffuse through the plastic - eg. Diesel oil.
If you don't use it for underground water pipes in cities, you'll normally get complaints from homeowners about 'chemical smelling' water, particularly first thing in the morning when water has been sitting stationary in pipes all night.
There is a test for plastics where they weigh a block of plastic then soak it in water and weigh it again. For some plastics the gain in weight can be a few percent.
Barrier PEX (often referred to as PEX-Al-PEX) uses a layer of aluminum, not copper. A far more common type of barrier PEX uses a low-permeability polymer coating.
I still have a length of it in storage but I don't know the brand by heart. It was pretty expensive stuff and it needed weird fittings, which were also expensive, the inner liner was blue, that much I do recall. In the end I mostly regretted going for plastic, I'd probably use regular copper pipe and crimp fittings again, less hassle and I'm just more familiar with it.
Do you mean PEX-Al-PEX? It’s mostly obsolete now, in favor of “oxygen barrier” PEX. The latter is generally approved for potable use, but there’s no reason to use it. It’s intended for closed-loop heating or cooling systems that contain non-stainless iron alloys, and the idea is that any oxygen initially in the water will be rapidly depleted, and deoxygenated water is not corrosive.
Probably alupex "meerlagenbuis"? Comparing it to copper it seems to be much more affordable per meter. I worked mostly with copper in the past, but did some work with alupex on my brother's house a couple of years ago. It's much more convenient and affordable than copper!
