Milk Stork Pump, Freeze, and Stash coolers are designed to maintain the temperature of already refrigerated or frozen breast milk. They do not bring milk to frozen or refrigerated temperature, they simply maintain it. They do not use gel packs or dry ice, and there’s no need to refrigerate or freeze the cooling units prior to use.
Milk Stork refrigerated and frozen coolers use different technology therefore are not interchangeable, meaning you cannot put refrigerated milk in a frozen cooler, and you cannot put frozen milk in a refrigerated cooler.
The refrigerated (or Pump) coolers rely on the principle of evaporative cooling, continuously evaporating small quantities of water at low pressure over hours and days of operation. Water flow within the cooler is regulated – responding to ambient temperatures – which protects the cooler’s contents from external temperature fluctuations during shipping.
The frozen (or Freeze/Stash) coolers rely on high-performance vacuum-insulated panels that line the inside of the cooler to work off of the frozen breast milk placed inside the cooler that will maintain the frozen ambient temperature for 96 hours. Frozen coolers have to be completely filled in order to maintain the frozen temperature.