Pour crushed ice into a hot water bottle

 

Fill a hot water bottle with cold water and crushed ice cubes. If your ice cubes are too large, put them in a plastic bag and break them with a heavy object.


Put the water bottle in the refrigerator for another 10 minutes to cool it down further. Take it out and place on the back of your knees or to bed and place it by your feet.

How effective? The bottle kept cool for about two hours. The only downside is the mild condensation, so wrap the bottle in a thin towel first.