Ice Packs vs. Dry Ice
Which should I be using when shipping perishables?
First of all what are the characteristics of Dry Ice?
Dry ice is formed by putting CO2 gas under pressure. The resulting material is a frozen solid that in this state is -78.5 C or -109.3 F. The product is typically available from suppliers in various sizes of block, pellets, or snow. It is good to keep in mind that dry ice sublimates (turns back into a gas) rather than melts (which also means little or no residual moisture). The speed of sublimation is tied into surface and cubic density area, so pellets and snow with far more surface area and less density will sublimate faster than block. Caution must be taken in handling dry ice, as the frigid cold can fairly quickly burn skin if handled improperly.
Likewise, what are the characteristics of ice packs?
Ice packs are also commonly called gel packs, ice bricks, or phase change materials. Typical ice packs are water and polymer gel based, or in the case of bricks saturated floral foam, and then sealed in poly bags. Most ice packs and bricks have a phase change point around 0 C or 32 F, which would be the temperature point where the material transitions from a solid to a liquid or vice versa. Less common, and more expensive, are packs where the material has been combined with fats, salts, or other chemicals to change the phase change point higher or lower.
So which works best?
The best results will largely be dependent on what the goals and shipping payload are. Plus dry ice may be limited in both accessibility and affordability to those businesses near larger urban areas.
If a product is perishable but can not freeze, dry ice is usually not an option since it is so cold. Products such as pharmaceuticals, fresh meats and produce, chocolates, etc…. would typically fare much better with ice packs. And sometimes a room temperature ice packs can even be added to a shipment in winter months to add additional thermal mass to a the payload, this helps slow temperature change, and can prevent a very delicate payload from freezing.
Products that are already frozen can ship with ice packs, though the ice packs only add more frozen thermal mass to a shipment to slow the thawing process. Keep in mind that most water based products and ice packs, even when frozen much colder than their phase change point, are not stable there. Once removed from a freezer, they will quickly radiate off the excess cold till the reach their sustainable 32F/0C phase change range. A product such as ice cream, which typically must stay colder than frozen water to stay hard will not do so for very long with common ice packs.
Most frozen products tend to ship better with dry ice, which will actually freeze the product even colder, and store thermal energy within the payload itself. It tends to be ideal used with ice cream products or sorbet or frozen meats and seafood.
What else do I need to know ice packs and dry ice?
- Regardless of refrigerant used, it is a component in a successful shipping strategy. The shipping container, shipping point, destination, seasonal conditions, and the payload itself are also all of major consideration.
- Sometimes an ice pack is too cold coming out of a freezer to be used immediately with temperature sensitive cargo and needs to be set out first to burn off extra cold. This is traditionally called conditioning.
- Adding a Thermalast liner bag to an existing cooler can extend the safe transit of a perishable shipment by 2% to 40%
- While ice packs still take up space and have thermal mass to slow temperature change even after they thaw, dry ice in time completely disappears. Once it is gone the payload is on its own.
- Most companies underestimate the amount of refrigerant required in a shipment. Most ice packs perform little better than ice. So while someone would not consider putting a couple ice cubes in an overnight shipment, they might think and ice pack of equal size will. This is a good formula for failure.
- When considering what size and how many ice packs to use in a package visualize 2 glasses of iced tea on a warm summer’s day. One has a large chuck of ice, and the other has crushed ice. Which do you think will stay cold longer? Same principle goes for ice packs. Fewer and larger typically outperform many and smaller, often costing less as well.
I am interested in developing a perishable shipping system for my products ….what’s my next step?
Please contact our expert sales team at 800-228-9506 or email email@example.com. We will assist in determining the best method and materials for your project and offer samples for your approval. Testing may also be recommended to assure the performance.