Yes, but exhaust fumes then weren't as concerning as they are now. (Speaking from experience!) Every car produce exhaust and there were no emission controls. And with a modestly tuned 850cc engine and a pea-shooter tailpipe, the Mini was hardly noticeable.

I dont think this foam does much, might help keep out some gas tank fumes right after you fill up, and might damp some drumming of the body side panel.  I wondered about that notion of trapping fuel fumes.  One of the original advertisements for the Mini showed it full of happy happy people, more luggage than the boot could hold so the boot lid was open with a stack of luggage strapped to it (which is why Minis had the hinged license plate); driving with boot open would cause air flow back into the trunk, occupants would smell fuel, so Uncle Alec said lets stuff some foam in the gaps.



For me, originality is nice but this one is no show car, I want it to be a Qship with more go than show. Nicer presentation will be important on my Riley Elf if I can ever get started on it, but not on this Cooper S because the foam is hidden by the two tanks.  What do you suggest using?

Can we be a little neater in the presentation or are you after the original factory look?

  about 10 inches of foam is visible in this shot of an Elf boot

There are several non mini options. AC window  sash foam Black. The swimming pool noodles, maybe you can match the color of your car, if you go this route. Plumbing water pipe insulator and other stuff. Pun intended. IMHO, I think the spray foam is too messy in spray and removal. Very hard to control, but great for what it does. 

When I was tidying up my mid-80's Mini I found the bottom liners in the companion boxes to be distorted by moisture. On deeper inspection, I found openings from the bottom of the boxes into the sills. Part of this exploration was to try and reduce the ingress of exhaust fumes. Above 40 mph/60kph I had to close the windows. Much better now!

There are several versions of spray foam. You can get low expanding spray.

If you can, find a closed cell foam. Open cell works like a sponge and absorbs water. Mini also came with a ring of foam around the fuel tank neck, which causes the neck to rust through.

I wonder if anyone has successfully used spray foam insulation to fill the gap. I'd be tempted because it produces a closed cell foam and will get into the deepest, narrowest part of the gap. Use it sparingly as excessive foam may push out on the body side panel.

Maybe there's an automotive version of spray foam insulation.

thanks, I will see if I can find a local source.

I believe it is just upholstery foam. No glue, cut from strips and shoved into the gaps between the boot and seat back bulk head. I've never seen greenish, just what you pictured.

found some old filler strip foam, pretty sure it was packed in the gaps at the sides of the rear seatback, long time since I took the car apart.  I think it might originally have been soft and greenish in color, its hardened and brownish now that it is almost 60 years old.  I dont know if it had an adhesive edge or if adhesive was applied to make it stick in place.  What is it or what do I get to replace it?