Iceland coolers have extraordinary cooling properties through choice of manufacturing materials and features such as the pressure release valve which allows for purging without opening the lid, thus mitigating loss of temperature.
To get the very best from your cooler for long term cold storage we recommend pre-chilling the cooler to avoid using your pack-ice to make the initial reduction in temperature within your Iceland cooler. This is best achieved by freezing two water filled gallon milk cartons and leaving them in the cooler overnight, and then removing at the time you pack your Iceland cooler for travel. A pre-chilled cooler can be expected to hold it's temperature below freezing for at least a week (up to 9 days in our field tests). Obviously, once opened or left open, the cooling properties may be compromised depending on the ambient temperature.
For maximal effective cooling time, such as on an extended camping or hunting trip, store items in a large (45 or 75 quart) cooler and open it once a day to replenish a smaller "day use" cooler (20 quart).