... spa are certified to CE, ROHS ,SAA and ISO producing standard- OUTDOOR SPA,HOT TUB,WHIRLPOOL SPA,SPA,OUTDOOR WHIRLPO Knight ... of closed-cell, high-density foam insulation to the underside of the spa shell before the plumbing is installed. This insulation ensures a ... a rugged, yet aesthetically pleasing foundation that truly seals the bottom of the spa, locking in heat and sealing out moisture, a ...