Patented Rigid Bond Shell Construction, this industry first was accomplished in 1988. Innovative three-layer Rigid Bond patented shell provides superior strength and thermal retention qualities that make Sundance Spa shells the strongest in the hot tub & spa industry. Acrylic layers are available in a variety of long-lasting colors and textures to match your style and environment. The shell is shaped from one seamless piece of acrylic. Easily cleans and feels great against your skin. Vinyl ester layer is applied to block vapor and moisture, forming an inseparable bond between the acrylic surface and the rigidizing layer. The bonding layer virtually eliminates the possibility of blistering, cracking, or delaminating. This allows our spas/hot tubs to withstand ambient temperatures much higher than other spas/hot tubs. Special resins designed for structural support that is used in the aerospace industry are at the heart of the proprietary rigidizing process. The bonding and rigidizing layers are hand applied to create a Sundance Spa shell 8 times stronger than ordinary spa/hot tub shells.