Waterproof door liners

[trashbat]

I had to do some work (ahem, fishing out the bolt I dropped) on the inside of my Alfa 156's door today. In order to achieve this I cut up part of the foam membrane that previously covered the entire door and I'm told protected the door card from moisture.

No idea what I mean? This white stuff: http://www.kalisz.mm.pl/~Perlus/166/cos/1.jpg

How much do I need to care about the integrity of this thing?

If the answer is 'enough', what can I use to (a) replace it, (b) bond it, and not necessarily in order, (c) remove the old adhesive that will probably make this job difficult?

I looked for closed cell foam but it's more difficult to buy than I was expecting.

[trashbat]

Thanks all - hard to tell if anyone else has issues with it, doesn't seem to be any obvious cases. I did give cutting through the adhesive a go but got nowhere and didn't think about the purpose of the liner at the time.

I found some 3mm closed cell foam in the end so I think I'll give a repair a go.