Cold:
They work well, but be certain to cover them with cloth before applying to your skin.

Hot:
Worked well "¦ at first, but then I heated one for 10+10+10+10 seconds and it blew up like a balloon. That stretched the plastic out of shape, making that pack useless now. Also, they are a pain to heat up "“ because you have to do them 10 seconds at a time & massage them "“ you need to be careful massaging the corners, because those get especially hot "“ and the resulting heat does not last long. The fact that the heat fades quickly is part of the reason I wanted to get it as hot as possible, and why it expanded. I did find that the warm packets work very well in a clean, damp sock for moist heat.

Bought for use with Google Daydream View VR headset and Moto Z Droid. Works great! Fits nicely behind the phone in the headset. I have only tried it with the pack at refrigerator temperature so far and it kept the phone nicely cool for the first 20 minute test. Without this pack, the phone would be very hot after 20 minutes. This should make the Daydream usable without overheating the phone.

I must qualify this review by saying I bought these to keep cat food colder in an automatic feeder dish. Unfortunately, they are not useful for this purpose so I'd discourage others from using them as such. They do not freeze solid and don't stay cold for very long - only are cool for about 15 min. I wish someone would have said that in the Q&A section because if I'd seen that, I would not have purchased them. Just now I added an answer to that question so others would not make the same mistake I did. Had I ordered them as cold packs for injuries, swelling, etc, I'd have indicated a stronger preference for them.

I got these for use with my Samsung Gear VR to help keep my phone from overheating while using it. They work really well for that. They're a great size and fit easily between my S6 Edge and the Gear VR plastic cover. It stays in place and doesn't add much weight at all to the unit as a whole. If you're having overheating issues with your phone and Gear VR, give these a try.

Just like a lot of other people who purchased these, I purchased them for my Samsung Gear VR. I own a Galaxy S6, and it gets to very hot temperatures and thermal throttles; something you don't want while in VR. Because these are very small packs, they fit between your phone and the Gear VR's front plate, although I find it challenging to fully mount the front plate in some cases. If you squish the pack, it'll snap into place fully, but if you don't it'll mostly snap into place (some mounting points won't make full contact, but that's okay because it shouldn't fall off.)

Because I live in a highly humid area, condensation is a problem. To remedy this, I rip off a piece of paper towel and place that between the pack and the back of my phone. Condensation still occurs on the front plate, and if you don't wipe it off every once in a while it'll start to drip. Because there aren't any electrical components on the front plate, I don't find myself wiping it off often because it's just water.

As for play time, I get at least an hour out of these before the pack gets warm. Even then, heat will transfer to the pack and away from the phone further preventing thermal issues. I've only really tested this for an hour currently, but you can probably squeeze an additional half hour. Although, these come in a six pack, so if you stick them all in the freezer you can just replace the warm pack with a freshly frozen one. If you want to limit the condensation, you can also stick them in the fridge, but you probably won't get the same results as if you freeze them.

I'm happy with this purchase, and I'm thankful I looked to the internet for other people experiencing thermal issues with their Gear VR. I don't expect to have any more thermal issues in the future thanks to these ice packs.