So, there's pvc-coated nylon, and there's neoprene. Probably, the skill of the person running the sewing machine that makes each piece is maybe more important than the material itself, as to whether it will leak, or not to leak ...... that is the question? ...
This
https://en.wikipedia.org/wiki/Neoprene has good info.
One thing fo sure, when it goes leaky, you know it ..... is very, very cold.