My wife liked it hot, and I sweated my [censored] off for about a year, no covers to keep the heat in! Had no mattress pad and just a sheet over the vinyl. One night I rolled over and sploosh, my elbow went through the vinyl that had gotten brittle because of how hot she wanted it! Luckily the sheet kept me from going full bore into the water, but what a freakin' mess! That is when we started using a mattress pad under the sheet, and turned down the temperature. The dual mattress system wasn't available yet, but as soon as it became available we bought it. My side is 20 degrees colder than hers...