Yup, I'm not taking any notice of hydrogen filled jump bubbles because they contradict setting canon and are not part of T5 either.
In the DGP SOM it was a bubble of normal space, no mention of hydrogen bubbles.
This was misunderstood by a T4 author and fanon became canon.
TNE FF&S says this:
"Jump drives require fuel, displacement mass, and coolant, all of
which are collectively called jump fuel (liquid hydrogen being
used for all three functions)."
T4 FF&S says this:
"Once in jumpspace, the jump drive maintains a small
bubble of real space around the ship, using power input to
the jump drive from the power plant (0.018MW per cubic
meter per jump number). The fuel remaining in the jump
drive's surge tank is used to create a thin hydrogen atmosphere
around the ship during jump, which helps to delay the
collapse of the jump bubble"
which it immediately contradicts in the drop tank section with
"Drop tanks are possible since the fuel is entirely consumed
before jumpspace entry,"
Note that collector powered ships don't use hydrogen to jump, and neither do antimatter powered drives.