Thermostatically controlled to help maintain pet is body temperature (100-105°F). Constructed of durable, weather-resistant, high-impact ABS plastic. Custom built-in red indicator light shows when unit is operating. Heavy-duty anti chew cord protector. Designed for indoor or outdoor use on hard, flat surfaces. Includes faux lambskin fleece cover.Small measures 13×19, 60 watts; Medium measures 17×24, 70 watts; Large measures 24×29, 100 watts.