My point wasn't about proprietary tanks leaking by permeability. But that Hydrogen leaks through materials and joints better than anything else can, because the molecules are the smallest in the universe. Sub-atomic particles are smaller but that is irrelavent here.
In the UK, for plumbing hydrogen lines inside a building, we had to engage a specialist contractor with certification, at a high cost, to install the system. The Co tractor fitting-out the lab didn't have that certification because hydrogen requires such special controls. Gas piping could be steel, copper, etc. But hydrogen must be seamless steel tubes with metal to metal joints, etc.
On fuel tank so we used helium leak testing for the plymer tanks. The smallest inert gas molecules that permeate most plastics.
I don't know, but have an idea that Hydrogen carbon fibre tanks have a layer of aluminium foil, as the polymers would leak without it. Like crisp packets and other hermetically sealed wrappings.
But don't quote me. DO YOUR RESEARCH. CHECK REGULATIONS. They are there to keep everyone safe.
K2