We have a cal. King Sleep Number bed, one of the first ones.  This mattress pad is thick, plush and more than large enough for a cal.king. In fact, the thickness goes over the side edges so its pads every inch. It stays cool and I sleep better.  This arrived on time in a huge box and was well worth the price. A cloud of comfort.  My only concern was the banding that holds it on is light on the elastic, yet with the sheets it stays put. A week later, it has not shifted. I'm very pleased.