left in the freexer overnight, nearly burned my hands from the cold moving it to the insulated box in the morning. Combined with a sytrafoam box kept perishables safely cold for shipping even with a delay in delivery.

Unfortunately, it didn't work for me. I stuffed three of these in a large ice-chest with three tubs of ice-cream, a 24lb bag of ice, one block of dry-ice and the next morning, these were thawed out. Thank goodness I had more ice and dry-ice with me the next morning. Maybe they work for a really tight and smaller ice-chest but it didn't work for me. I returned the product for a refund, great customer service! For that I gave it an extra star.

I'm giving this product 3 stars but would love to make it 5 if they made the casing thinker and stronger. I used these ice packs on a recent work trip to keep breast milk cold. It certainly did the trick but some how two of the bricks were punctured! I'm not sure how this happened since all I had in my cooler were bags of milk. Unfortunately, plastic bags are not long enough to hold the bricks so you are kind of SOL. If they changed the packaging to a more durable material, 5 starts all the way. They kept my milk nice and cold for two days!

This block is big and fairly thick. If you're looking to keep a small lunch box cold, I suggest one of the smaller sizes, like this Polar Tech RB15 Re-Freez-R-Brix Foam Refrigerant Pack, 4-1/2" Length x 4" Width x 1-1/2" Thick (Case of 6).

I pack one of these big blocks in my large lunch container (slightly smaller than a small Igloo type cooler) and when I get home from work it is still cold. They definitely stay cold longer than any other ice pack or gel pack I've owned. One word of caution though "“ the packaging is susceptible to opening at the seams, and if you're not careful, also tearing. I found this out one day when I saw some green liquid at the bottom of the lunch container when I was cleaning it out. I didn't want to go through the hassle of returning so I just super glued it tight. Besides that, these blocks work great.

Frozen bottled water are colder than these. I'm not sure which would last longer though. But the worst is the bags do not hold up after multiple uses. First use might be great, but once it punctures, the inside green stuff gets all over the place.