I'm planning to purchase a portable indoor infrared sauna to be located outdoors under my deck. Although ambient temperatures in the SF Bay Area are fairly mild, I am concerned that it might take quite awhile for the sauna to reach an optimum temperature of 130 deg F while using it during the winter months without adding some type of insulation. I've considered wrapping the exterior walls of the sauna with mylar space blankets and the roof with styrofoam or fiberglass insulation. Since the deck above the sauna is watertight, there is no concern of moisture coming in contact with the roof insulation. Would appreciate any feedback as to whether mylar would provide adequate insulation!
I use mylar windshield sunprotectors inside my cedar sauna. It seems to hold and reflect heat back into my "phonebooth". I use the two suction cups on the glass door and let it hang down. I have a second sunprotector I open across the botton, in front of my feet to reflect back the floor/under bench heater. I also have emergency mylar blankets gummi-glued to the side walls. All sounds tacky, but really just looks like I paneled the sauna. Can't hurt anything. Give it a try.