1967 911 - Material behind lower rear window corners causing rust

[CA-Don]

Upon stripping back seat area and removing rear window, preparing for body restoration I found rust in both left and right lower corners of the body. I appears insulation was installed (factory?). If the window leaks water into this area the material hold the moisture causing the metal to rust.

Any thoughts on what should I replace the material with or even if it is necessary?

See attached picture.

[savaden]

I would leave it out. It is factory. Cotton felt.

SV

[smedley]

It's a residual gene marker from the the original 356 DNA!

Virtually ALL of them do that if/when the window seal petrifies and leaks.

If you must, for sound insulation, try the aerosol expanding foam (Home Depot), and use a factory OEM rear window seal.

[Ivan Fuller]

Seem to recall the factory used the expanding foam idea in the front edge of long hoods at some point to reduce dents when the lid was being closed. The resulting rust holes from trapped moisture were similar to the cotton felt idea.....

[RSTarga]

If you want to avoid rust, use 1/8" closed cell foam. Nothing that absorbs water. I don't know how you would control the aerosol stuff, and it absorbs water.
You could also use one of the dynamat type products. Somebody mentioned Stoddard has a kit, but what material is it?