Previous poster's experience is common. Before it gets stuffy, it does seem warm, because the air is moist, and evaporative cooling of the bottom layer has stopped taking place.
Then the air cools, water vapor condenses, and DWR becomes certainly not Dry-Water-Repellent. It becomes durably water-retentive or definitely wind resistant.
Reflective defies known physical laws. A shiny sheet instead of a shiny bauble, but leaving you steaming in a partial bubble.