There was a "major manufacturer" that did a "quick and dirty" (not real scientific) test of the floating blankets and their engineer determined it added about R-10 to the overall insulation to the top of the spa (including a hard, standard insulating cover). My understanding is that they took a spa that was in a climate controlled room and did a 24 hour test with, and without the blanket, monitoring the overall kW usage of the spa.