*** This is Mattress / Floor Combo Thick Pad unit. This is much much much better than other companies thin pad. Make harder and cost more ship. therefore all other similar product use easy shipping thin pad. but they are much less quality and you don't get same temperature and keeping warmness as this THICK Pad. This hot water mattress pad is very unique yet used by Korean for many many years. It came from concept of use hot boiled water through copper tube under house floor, which makes floor to be heated to control temperture of house, not using air heat which dry your skin. Using this pad will not only make you calming and soothing in bed but help your muscle relaxation and take away your back pain and neck pain as well. Ask any Korean friends. They will tell you how good this is. There is a controller that control temp. and automatic shut off function. You only need to fill water once every 6 months or so. Once you fill during winter use, you are done.