Tests have shown that it is actually irrelevant which side of the rescue blanket faces the injured or hypothermic person: There are no significant differences between the silver or gold side.
In short:
If a person is to be protected from (further) cooling, they should be wrapped in the rescue blanket so that the film is between the lowest and the overlying layers of clothing.
However, if a person needs to be cooled, the rescue sheet on the body is useless. However, it can be used as an effective awning to provide the person with shade.
However, the golden side of the rescue foil definitely has one advantage and benefit: to draw attention to itself, it is more visible from a greater distance.