... Gosh, i feel silly posting this now, lol. ...
Why, TC? — surely asking questions is what the GMB is all about!
Anyway, when I saw your pictures, I thought that it was a rather nice homemade hot water bottle, probably WWII when such luxuries would have been unobtainable, but string probably wasn't rationed*. Indeed, while contemplating the pleasure of warming my cold feet on it, I fell fast asleep, so it must be so. Q.E.D.
Next question?

Bernard C.

* — Fond recollections. One of my earliest memories of Grandad Cavalot at 24 Cheney Manor Road, Swindon, was being put in charge of string in his garden and allotment. It was my job to extract every scrap of string from the sweet peas, runner beans, or whatever, undo the knots, wind it up into little hanks, and put it back in the string box. He also taught me how to tie knots. Yet another set of skills lost to today's children.