HotSnapZ Reusable Hand Warmers & Body Warmers - Instant Heat Packs

These are cool little devices. Bending the metal disk with your thumbs activates the reaction which causes the liquid gel to solidify and heat up. It gets to a max temp of 130F. I purchased them for scuba diving and tested them out with my wetsuits in a pool. When I placed one against my abdomen (over a bathing suit, under a wetsuit and in water), it was very warm and did leave a red mark on my skin (which went away). I used the large one between two layers of wetsuit on my back, and it was comfortable. Also small ones fit nicely in my armpits and were not too hot because they were not pressed against the skin like the abdomen one was. Because the water moves around in a wetsuit, the heat didn't last very long (maybe 15min) but I'm hoping it will be enough to make a chilly dive more comfortable. There is no way to activate these through the wetsuit, so you have to activate them then gear up and get in (would be perfect if I could activate one near the end of a dive). They become quite hard once activated, in whatever shape they were when they were activated. The heat lasts much longer when insulated and dry, for example in a jacket pocket.Things I learned: Although there are microwave directions on the website, they are much trickier than the boiling method. I damaged one in the microwave. I recommend sticking with the stovetop boiling method. I was also having a problem with them activating on their own (after a week of sitting on the counter, while I wasn't even home so not touched). Ray from the company was extremely responsive and helpful with these problems. He explained that the self-activating was due to not boiling long enough so there was an invisible rogue crystal left that at some point randomly triggered activation. He recommended boiling longer, and/or letting the HotSnapZ cool in the water to be sure everything is completely dissolved. That seems to have worked. He also replaced one that arrived damaged quickly and generously (adding extra free ones).Customer service is outstanding, Ray really stands behind his product. My kids are stealing them every evening to use after swim practice!Update: I have now used these scuba diving, and they work REALLY WELL under a wetsuit when placed in the armpits. It is so cozy to dive with a warm core, and the wetsuit insulates the heat for the whole dive. And, they can be recharged by boiling in the hotel coffee/tea pot.

The company calls this a chemical reaction, but it's actually even cooler than that, because a true chemical reaction would not be perfectly reversible and these would degrade over time. What's actually happening is that you're taking a salt solution (like table salt, but a bit different chemically) and putting so much in there that it's happy being dissolved at boiling temperature but wants to crystalize at lower temperatures. Since they put it in a sterile bag there's nothing to cause it to form crystals until you snap the disk (and don't ask me why that works, but I've read that it forces particles into the solution). Then the whole thing spontaneously forms a salt crystal inside the bag, which is really fun to watch. And it gives off a lot of energy similar to what happens if you bring two magnets near each other and let them snap together.In theory, these things will last as long as you don't damage the plastic bag and cause a leak. All you're doing when you reset them is redissolving the salt back into the water. And if it does leak, no big deal. It's just effectively salt water with some food coloring.The only downside to these versus standard heat packs is that their heat is more intense but shorter. Some of this is because there's probably just not as much potential energy in these as in the standard chemical heat packs, but also because the energy they release gets generated all at once rather than over a period of hours. But it's absolutely worth it to never have to buy another heatpack, and not feel bad about chucking a bunch of plastic in a landfill every time you use one.

Hand warmer work well in 40 F weather but only stay hot for 5 minute and warm for 15 minutes. Worked well to unfreeze hands so didn't have to wear gloves so we could using phone for photos outside with no gloves.

My MIL(60s) burned herself by over using these on her shoulders when she seemingly irritated her rotator cuff, the heat did help at first until the burn occurred(she used one every night in the same spot for a 4 days). No burn has occurred on her elbow when she uses these for plasma donation comfort twice weekly. My husband(29) and I(31) have used these no problem regularly for about a month. When we first got them shipped they seemed slow to react but after the first boiling they have been triggered with ease. All my set was as described and functional. Silicone tongs are a must for fishing these out of the pot because they are slippery, boiling hot, and the plastic thins/stretches during the process of deactivating them. They also stay hot for a good while after getting them out of the boiling water.I am very happy with these, just remember everybody needs to pay attention to their own temperature limits.ETA 3/28/2022Husband has now lightly burned himself with the pads, Cover with a towel as sometimes they just continue to warm up past comfortable temperatures.These still work great with weekly boilings(we wait until we can do the full box or at least all the small ones for a recharge). And we're looking into getting more small ones.