Arctic Diving Gear

Holding jump lets you swim upward through any liquid instead of struggling against it, your breath lasts far longer and drains health much more slowly once it runs out, and you get proper grip on ice so a frozen cavern stops being a skating rink. On expert and above it also blocks the chill you pick up from stepping into cold water, which is the difference between exploring a frozen ocean and stopping every few seconds to wait out a slow.

It glows around you while you are submerged, and that is what actually makes deep water navigable. Torches do nothing down there and most light sources are awkward to carry while swimming. Out of the water the glow drops to a faint shimmer that is decorative rather than useful.

Any headpiece hides it, including a purely cosmetic one in the social slot. That is display only and does not switch anything off, so wear whatever helmet you like unless you want to see it. Stacking other diving equipment alongside it does nothing at all, since none of the breath effects add together.