Accommodates 1- or 2-gallon jars as it wraps around them and provides a supply of warmth. Four settings: OFF (when ambient temperature is above 75-81ºF), LOW (when ambient temp. is 71-73ºF), MEDIUM (when ambient temp. is 66-70ºF) and HIGH (when ambient temp. is 60-65ºF). Waterproof and designed to be left plugged in or on for indefinite amounts of time.