Wonderbag is a draw-string bag that’s overstuffed with repurposed foam chips:
After bringing a pot of food to the boil and placing it in a Wonderbag, the food will continue cooking for up to eight hours without any additional energy source.
I love my Wonderbag. It makes particularly great curry. I associate slow cookers with overcooked ingredients but Wonderbag is different (and unpowered), leaving vegetables with their bite and protein in one piece.