The underlay heats up just fine. TIP: for it to work, it needs to be under the covers. I was trying to see if it works, I put it on the bed, turned it on, it didn't heat up, and I thought it was defective.... They don't clarify this in the instructions

We bought three of these mats. We plugged them in for almost half an hour, testing all three settings. They never got warm. They emitted a very faint heat, like a 10-watt bulb when you bring your hand close to it. Because we saw the very good reviews, we bought three pieces with relative confidence from the start. It might have just happened to us or it could be the store's fault. But all three are problematic? What are the chances?

Very good and very warm (due to fleece), heats up relatively quickly, the resistance is not noticeable..

So far, I love it. Very toasty and feels good on my muscles. UPDATE AFTER TWO MONTHS: One side no longer turns on and doesn't heat up. Too bad. Expected it to last more than two months. :(

The most important thing is that I am not bothered at all when I touch metal structures when I lie down, like the radiator next to the bed, which with other brands was very unpleasant. I don't realize that it is in the bed. On one side, it is warm enough for men.