What type of insulation is used in the casing of a Beachcomber hot tub?

Every available space is filled with Icynene foan, wich has a high R value of 3.6 per inch - the higher the R-value, the greater the insulating effectiveness. It expands as it is sprayed, filling 100% of the hot tub's cavity. This completely seals and encapsulates all of the open space inside the hot tub cavity and prevents moisture or air to penetrate the vessel of the hot tub. The water in the tub is then protected from heat loss, much like a well insulated house.