We made an insulated shelter from a cardboard box and styrofoam and placed this 16 inch by 18 inch heating pad inside. The results were excellent.Our box measured 17 inches by 20 inches by 9 inches tall, so the heating pad fit nicely inside. We duct taped 1” styrofoam sheets to the outside walls, roof and bottom. This insulation probably brought the box to an R value of 5 or less…not a lot, but sufficient to guard against wind and retain some heating pad heat. We placed the heating pad on the inside floor of the box and added a polypropylene blanket and wool pad to the heating pad to make it cozy (see photo).We placed a temperature sensor inside the box, NOT in contact with the heating blanket and got these results in the unoccupied shelter:outside temp (OT)/inside temp (IT)/control setting (CS)OT36 IT48 CS1; OT32 IT46 CS3; OT29 IT48 CS5; OT27 IT52 CS6.The shelter was placed in a dry location, away from the wind. Humidity was high, around 70-90%.When it got close to freezing, we increased the control setting to 5 and 6.We were amazed by how much above ambient temperature the small sized heating pad raised the interior temperature. The small 16”x18” pad only uses 55 watts on the highest setting (6). Running it all night for two consecutive nights of freezing weather used less than one kWh (0.589 kWh), so quite affordable to keep our outdoor cat safe in extreme weather.The control timer has 4 settings - 4hr, 8hr, 12hr and 24hr, and automatically turns off after that time. We needed to restart the 24 hour setting each day. We plan to keep this shelter in a dry location since further improvements will be needed to waterproof it. The heating pad is a great product we are recommending to protect outdoor pets from extreme weather (and from others descriptions, this is a great sleeping pad for indoor pets).