I don't know if it reduces the heat that much since my car tends to stay cool in the summer and warm in the winter.
As far as where to put it I took everything out of my car and put it where ever I could. Best choices are to take off the door panels and to put it there. Underneath the carpet in the car and in the trunk. It's pretty much up to your personal preference. I would start at the doors and go from there
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