We bought this for our 8 months old to sleep on while camping. We put it under the fitted sheet in his pack n play. It kept him nice and warm and really took a load off my mind. We took off one star because the quality of the material was less than what we expected but as far as functionality it worked great for our purposes.
Its very thin and seems like it would be very easy to break, but since it sits under the sheet its not really a worry. As soon as you pick up the material you can notice that it heats up your hand. Its a somewhat strange sensation at first because its not hot in the typical sense. Normally when you sit somewhere for a while, the surface is warm to the touch because the surface has absorbed some heat from you. This is an altogether different feeling. The material seems to not absorb your heat, but reflect it back at you.
Although its a strange sensation to directly hold the material, my son seems to love it in the playpen. He really didn't like sleeping in the playpen (he seems to be very sensitive to cold) but once we added this he has no problems staying asleep. When I pick him up his back is noticeably warmer. The warmer is sort of like aluminum foil, but much sturdier and less crinkly/noisy. It has a thin foam applied across it which I assume is to act as an insulator, but it does provide a little extra bit of cushioning as well, which is nice.
Overall I am happy with the product and it seems to work as advertised
This product actually did seem to keep our daughter warmer. It is very similar to an emergency blanket, but less noisy, as the material is a bit softer feeling. We no longer have issues with our daughter waking up cold and coughing. Good, simple product.