It has to have a means of carrying it over the arm - Mum needs both hands to get out of her chair, and then doesn't want to have to bend over to pick up the hot water bottle. Being able to loop it over her arm to carry it is important. In addition, one side has double wadding, the other single, so that she can have it one way round when it's just been filled, and the other when it's cooled down a little. I really don't want to change the design since it is so tailor made for her needs!