All you do is boil water and stick them in to warm them back up.I reuse mine all the time and 2 yrs later they are still working.I must have 30-40 of them now.And they work great.
Boil them?
UniHeat package list contents as: Iron powder, water, active carbon, vermiculite, wood powder and salt.
If it's that easy I'll keep all of mine too.