The Dog Palace is a rotationally-molded plastic house. All panels of these products are filled with recycled ESP foam (commonly used as an insulation material in construction). To demonstrate the real value of insulation, we conducted an experiment on the Dog Palace with and without insulation. (Note: This product is only sold with insulation and door.) The results of the experiment reflect the heat retention inside the Dog Palace using a common 100 watt light bulb (no other source of heat). At an outside temperature of 40°, the insulated Dog Palace will be 70° inside, while the Dog Palace without insulation will be approximately 45° inside. At an outside temperature of 0° degrees, the insulated Dog Palace will be 30° inside while the Dog Palace without insulation will be approximately 4° inside. An average dog's body heat will raise the temperature inside the Dog Palace 25° in the winter without the floor heater (sold separately, available on samsclub.com); therefore, if the outside temperture is 25°, with an average dog inside the Dog Palace the temperature is approximately 50°. The Dog Palace is very easy to assemble and takes very little time. The easy pass-through, self-closing door design keeps the wind that reaches your pet to a minimum and closes itself. The specially-designed door is made in two pieces - the bottom half is removable for initial training if needed. The Dog Palace is sized for medium to large dogs (Lab through small St. Bernard). Another unit available on samsclub.com - the "DP Hunter" is sized for small dogs (beagles, basset hounds, pugs, etc.) or cats.