When iron rusts it gives
off warmth called oxidising heat, but you cannot feel this heat because
its oxidising rate is too slow.
If this is speeded up, more heat is produced. This is the
principle behind MYCOAL WARM PACKS.
The warmers are activated by removing them from their protective
airtight packaging to expose them to air. The blended ingredients of
iron, salt and water, combined with the oxygen from the air, causes the
rapid oxidisation of the iron particles. This reaction produces heat.
The heating temperature and duration are controlled by the
amount of air ventilation, which passes through the many tiny holes on
the inner packets. The duration of the reaction is finite and the
warmer should be disposed of after it has cooled.