HOT LINE heating pads are packed after production in liquid state (transparent). While transporting and shelf storing, it is advised to keep the pads at a temperature higher than 0 degrees C. Once heating pads in liquid-state, freezes abruptly, the Sodium Acetate may be triggered (the same as flexing the metal disk) to crystallize, releasing heat.  The heating pads stiffen and turn opaque.

No damage is caused to HOT LINE heating pads if they freeze.