Okay- not forever, but 10+ hours for sure with no protection from the elements.
Sure, you can use them in a cooler for easy cooling without costly bags of ice that only last for a few hours with a few easy steps and a couple of bucks.
We use it for transporting meat and to cool meat rabbits and farm animals during the summer months.
Step 1: Gather Your Supplies
* 3" PVC but any size will do depending on your cooking needs. I got a 12' piece though I only needed to make 7 of them. Too bad I forgot to take a picture before I cut them into 10" pieces.
* 2 end caps (of corresponding pipe size for each ice pack
* PVC glue
* Good 'ol H20.