A Cultural History
I imagine that padded garment's a micro-meteor protection vest?
IIRC, the silver garment was worn during launches and landings or other "don the life vest" situations. The padded vest and helmet would be added if they needed to leave the ship, so the silver undergarment was probably pressure and thermal control while the vest provided micrometeor protection and served as a load-bearing harness for the life support system. Don't think it's canon, but it makes sense.