fyi, https://www.ebay.co.uk/itm/194...7:g:Pu4AAOSwbrlc-nEV
....maybe the closest thing available to the bitumen-felt .... 66 euro for shipping from Germany seems like a bargain these days..!
The bitumen-filz was used everywhere on the Goose, at least for interior padding and also on the rear bulkhead. I saw one comment, that bitumen for car interiors has been disallowed (legally) for car interiors, my guess its both toxic and makes a great candle...So closed cell foam is another option...Lee