Could Tyvek be used as a sort-of poor man's emergency Goretex(tm)?

Plastic bags are dirt cheap, compact, waterproof and trap some warm air around your body. However, it really bothers me that they also will soak you in your own sweat, likely leaving you worse off than before. Same for my beloved GI poncho or any of the space blanket variants.

I wonder how well a Tyvek bivy sack would work compared to a plastic one. Sometimes all you need is something to keep the water off and trap some dead air around your body.