Some temperature loggers must include the probe in a glycol or buffer solution to provide accurate and reliable readings. Certain vaccines require very low temperatures to stay stable; else they will start to lose effect. Hence, temperature probes are used to measure their temperature all day long. The probe is placed in a glycol solution to prevent variables like airflow or temperature loss due to the opening and closing of the refrigerator door. Glycol is preferred because it has a very low freezing temperature making it suitable to work within a broad range of temperatures.
CDC recommends the use of an air-probe or a probe designed specifically for ultra-cold (dry-ice) temperature monitoring as buffered solutions may have warmer freezing points.