1. Flex metal disc back and forth until crystals forms.
 

2. Knead pack to soften. The temperature is possible to reach about 50 degree (depends on the physical environment), if the heat pack desired to prolong the heating duration, it is better to cover it up with a thin towel.
 

To prepare for next use: 
 

1. Put the hardened heat pack into boiling water.
 

Continue boiling for approximately 5 minutes or until the crystals are completely liquefied.
 

2. When the pack cools down, it can be used again.
 

Warning: Do not heat directly in microwave oven.