I was asked on Shabbos the following question: Can hand warmers be used on Shabbos? Does it make a difference if it was activated before Shabbos or can it be even activated on Shabbos?
I was thinking, cooking is a chemical process of warming up non-food items on Shabbos to a temperature which may not be yad soledet bo should be fine. But then maybe it is like making a semi-fire. Then the issue may be Hatmana but that should also be for food items.
If anyone has thought processes to understand both sides of the questions, please help.