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ideas i've had lately are
highly perforated neoprene injected with nitrogen
dyneema UHMWPE jacket and pants with drydown inside or UHWMPE filament synthetic "down"
dyneema UHMWPE fleece (it's totally hydrophobic)
I suspect that the best overall option, if you are going to get wet no matter WHAT, may be well-ventilated neoprene or natural rubber injected with nitrogen bubbles.