Sorry, I cannot folow your arguments. They do not make sense and seem to contradict themselves over and over. Not sure of your background, but I have done some extensive testing of protective clothing in my lifetime if that helps.
No one is suggesting you make yourself an all metal wetsuit. However just like building insulation, your wetsuit is a sandwich with a radiant barrier overtop a mass barrier (neoprene). Also conduction and heat transfer are a factor of mass. The layer of reflective material is extremely thin and is againt a layer of very low thermal conductivity. It is not like it will accelerate the heat loss through the neoprene.
so note that when that metalized neoprene touch your skin with the metalized side it is not radiation or convection any more, it's conduction! and the metals are the best of the heat conductors!!!
No. It is not as if you have one or the other. Both radiation and conduction are always in play. So yes there will be some miniscule increase in conduction (a tiny amount of material bounded by a neoprene layer of low thermal conductivity) and some reflection of radiated energy. But the reflective layer is not a heat sump because of its very low mass, and it is bounded by an insulating layer
and if you look again, this time attentively, in the thermos bottle you'll see that bottle is metalized from outside and the main insulator is vacuumed gas between the two layers of glass. so no direct physical contact between hot liquid and outer metalized shell.
No. A thermos is glass, then metal coating on the glass, then the vacum barrier. The liquid is in direct contact with glass which is a very poor insulator. So it is in essence nearly direct contact with the radiant barrier.
end again, everywhere in home insulations or home appliances insulations the metal (e.g. aluminium) foil is aways outside of real thermal insulation (like rock wool or glass wool).
there is always a heat insulator between the source of heat (or cold) and reflective metal layer.
No again. Look at winter clothing that uses the reflective layer on the inside to reflect heat back in. If it was on the outside of your jacket it would reflect heat back out. That is why blast furnace workers and firemen have reflective barriers on the outside to reflect the heat out.
Again, as I have pointed out radiant barriers are not going to make a poor designed wet suit toasty warm. But they will provide additional warmth and the same principle is exactly seen in other application.