So I'm doing a bit of body work on my 1988 truck. At this current time, it is around the passenger side door. It's on the left hand side of the frame, which I think is called the B-Pillar.

Anyway I had to do a little work to remove the rust on the outer and inner section. There was very old spongy foam, that I needed to remove so I could do a thorough of removing rust. It was of a gray color, and had an appearance and texture of those kneaded artist erasers.

I'm not an expert on auto-body repairs, so I don't know what the intended use of the foam was, if it came with the truck, or if someone had added it in after.

If it is necessary to add a type of foam, after I am finished with my repairs, what would you all recommend? I don't want to grab just anything and shot foam into it, after all the work I've done. Especially if it'll cause moisture and or more rust in the future.

Is there a special kind of automotive foam that I should reapply when I am finished? I'm just curious if it's necessary to add it back in and what would be an ideal product for that.

Thanks!