The ChiliSleep devices should not be kept or utilized in temperatures below 32 degrees Fahrenheit (0 degrees Celsius), therefore slightly over freezing would be the chilly limit. In terms of temperature, the ChiliSleep system should not be utilized in temperatures over 100°F/38°C. If you attempt to utilize the system in temperatures near the extremes of this range, you may notice a significant decline in the unit’s heating/cooling efficiency. Use our system in a slightly chilly to slightly warm environment 55°F/13°C to 75°F/24°C for optimal results.