The cabbage leaf isn't intended to be there as a cooling agent. There's something about the way it either contains the body heat or to possibly off-gas of something therapeutic. I don't know *why* it worked, but for me it worked to leave it in for the day. I didn't ever need it longer. In case you were going to ask--I'm not aware that there is an exchange available with other cruciferous veggies--you can't stick broccoli or cauliflower or mustard greens (well, maybe?) in your bra for the same effect. And broccoli and cauliflower sometimes cause upset stomaches for the baby if mom eats them.