The ultimate must be along these lines

https://www.alpinetrek.co.uk/exped-waterbloc-1000-down-sleeping-bag/?aid=1de0fe5b72cc9ced63d2986e3bddb&pid=10004&cpkey=G9YEthUmuQKoWKSzojdj5GJortY858RWY8dJrfXs2MY&_$ja=tsid:60797|cid:775777833|agid:44715081590|tid:pla-146884569907|crid:185535913393|nw:g|rnd:11847355080708888648|dvc:t|adp:1o4|mt:|loc:9046172&gclid=EAIaIQobChMI0Z3wn4GA2AIVBxDTCh06jwqeEAQYBCABEgK9iPD_BwE