I purchased this icepack to treat some low back pain. It's a superb cold pack.
It is very cold for well over the 20 minutes my doctor prescribed for cold therapy. It is really big! It is also heavy, which I really like since the weight adds some compression that feels good on my back. You'll need a t-shirt or pillowcase between it and your skin. It's that cold. I wrap it in a thick towel. This will also help you keep dry.
I've used this icepack many times since I purchased it and there has been no loss of effectiveness. It is far better than ice in a bag or the flimsy cold packs that most drug stores sell.