Sapel Blog
3 Plastics That Withstand Cold and Freezing
It may sound strange, but like any other material, plastics differ in how much cold they can take. Every type of plastic has a standard minimum temperature. This figure marks the point below which the plastic loses its flexibility and structural strength. Below it, the polymer chains become extremely brittle and fragile, so your container can no longer take even slight pressure or the smallest knock, and it cracks easily. Below we look at the plastics that cope well with freezing, as well as the ones that should never be frozen:
Freezer-Safe Plastics
When buying or choosing a plastic container for freezing, just look at the bottom of the container for the recycling symbol (the familiar triangle) with the code inside it, or the abbreviated name of the polymer. These markings tell you whether you are dealing with a food-grade (food-safe), cold-resistant plastic or not.
1. Rigid Polypropylene (Code 5)
Polypropylene is one of the toughest, most durable and safest plastics for storing food, with excellent resistance to cracking. The biggest advantage of PP containers is their remarkable temperature range: they can withstand anything from a freezing 0 °F (−18 °C) to a hot 240 °F (116 °C) without the slightest change. The popular BPA-free snap-lock and screw-top food containers are made of this material and are ideal for storing all kinds of meals and soups in the freezer.
2. High-Density Polyethylene (Code 2)
High-density polyethylene is a rigid, very tough plastic with excellent resistance to impact and cracking. This polymer is built to withstand the harshest temperature conditions and does not become brittle in the cold of a freezer at all. Interestingly, HDPE containers can withstand an incredible temperature range of −100 °F to +190 °F (−73 °C to +88 °C) without structural damage. All kinds of jerrycans and bottles, including the 10-liter jerrycan and the 20-liter jerrycan, as well as some rigid containers for long-term food storage, are made of HDPE, which keeps oxygen out and stops food from losing moisture.
3. Low-Density Polyethylene (Code 4)
If you are looking for a more flexible option for your freezer that is just as resistant to cold, low-density polyethylene is the best choice. This plastic is softer than HDPE, but it has excellent resistance to cracking at sub-zero temperatures and never becomes brittle. Just like its big brother, LDPE has an outstanding temperature tolerance, from −100 °F to +175 °F (−73 °C to +79 °C). It is the main material in high-quality zip-lock freezer bags, flexible plastic wraps (heavy-duty freezer film) and flexible storage bags that seal snugly around food and stop moisture from escaping.
The Freezer Blacklist: Which Plastic Containers Should Never Be Frozen?
Polystyrene (Styrofoam)
Containers made of polystyrene, recycling code 6, which most of us know by the trade name Styrofoam, are among the worst choices for the freezer. Polystyrene’s chemical structure is such that it starts losing its flexibility even at normal room temperature (around 68 °F, or 20 °C). Put this plastic in a sub-zero freezer and it becomes very dry, brittle and fragile. Freezing food in these containers is not only unsafe; they also crumble under the slightest pressure or movement and shed plastic particles into your food.
Thin Polypropylene and Single-Use Containers
These plastics carry recycling code 5 (PP) or 6 (PS). Many of us keep empty yogurt, cheese or cream tubs for freezing food. Although these plastics are normally food-grade (safe for food), their single-use versions are not designed for freezing. These containers are usually made of very thin plastic. Thin dairy packaging becomes extremely brittle at freezer temperatures and cannot withstand the pressure of food freezing and expanding. As a result, the walls crack quickly and air gets into the container, ruining the quality of the food. In short, single-use plastic containers and thin packaging are not up to the job in the freezer.
