Curses.. Foiled again! The foibles of faulty .... what is it?.....
The gold brownish colour that you see is not true. That's a reflection of the wood paneling colouring. You can see the true colour in the section by the floor and if your guess was aluminum foil insulation / vapour barrier you would be right.
This home building product was used in the seventies in new construction and renos. It only resembles aluminium foil, but is much thicker with an internal layer of a tar waterproofing.
It was designed to be used as a vapour barrier and an additional layer of insulation at the same time. But it had to be installed correctly to work well. It was stapled across building framing on the warm side of the insulation like any other vapour barrier.
However, for the insulation properties to work the foil had to be spaced away (3/4") and not touch anything except the stud framing it was stapled on to. Then a furring layer was built over the foil on the studs and the drywall panels were attached to the furring. This created the 3'4" air space required on this side of the foil.
The no contact air space on either side was critical to its insulation function as a reflector of radiant energy. The reason for this the metal of the foil itself. It is such an excellent thermal conductor that if it is touching anything the heat transfer will be greater than any benefit realized by the reflection properties.
In other words if it touches it transfers more heat than it reflects so a heat loss is created. In the photo there is no furring. The paneling is in direct contact so there is no net benefit in having it there. This is why this product is no longer seen.
But of course its out there in homes and buildings. So when you're having a property checked you want someone who knows the technologies and understands all the systems that are there.