Science Tip | The 7 Major Grades of Plastics—Are You Using Them Correctly?

These items have a wide range of uses, including microwave-safe food containers (such as保鲜盒 and plastic takeout boxes), soy milk bottles, yogurt jars, juice bottles, water cups, straws, and more. Material category 05 is the only one that can be safely heated in a microwave oven, as it withstands high temperatures up to 130°C and has a melting point as high as 167°C.

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It's everywhere.

The small triangular symbol printed on the bottom of plastic containers

Classifying plastics into seven major grades

The 7 digits of the triangle symbol

They all represent a type of standardized plastic container.

Can you tell how to use numbers just by looking at them?

“01” — drink it and toss it right away; never, ever be tempted to reuse it a second time.

“01” stands for PET (polyethylene terephthalate).

Commonly used for bottled water, mineral water bottles, carbonated beverage containers, and more, this type of plastic can withstand temperatures up to 65°C but becomes brittle at as low as -20°C. If used to hold hot liquids or heated, it may easily deform and even leach harmful substances that could pose health risks—making it suitable only for warm or chilled drinks. Moreover, scientific studies have shown that plastic products classified as Type 01 may release carcinogenic compounds after being used for more than 10 months.

Therefore, once you’ve finished drinking beverages from Type 01 material bottles, never refill them with drinking water or food—doing so could harm your health and end up costing you more than it’s worth. Of course, if you plan to use them for crafting small handmade items, that’s perfectly fine.

“02” should not be reused in cycles, and it shouldn’t be used as a water container.

“02” stands for HDPE (High-Density Polyethylene).

Common examples include yogurt bottles, chewing gum containers, cleaning products, bath products, and medicine bottles. Cleaning and bathing products, in particular, often harbor residues due to inadequate rinsing, creating a perfect breeding ground for bacteria. Reusing these containers to store new items essentially means sharing your space with those germs. Additionally, the 4-liter bottles of Nongfu Spring—marked with "02" on the bottom—may look sleek and high-quality, but they should never be used as water storage containers. Prolonged use could even lead to the release of harmful substances over time.

"03" on food packaging—definitely don’t expose it to heat!

“03” stands for PVC (polyvinyl chloride).

Common items include water pipes, raincoats, plastic bags, and construction materials. Plastic products made from this material can easily release harmful substances—such as unreacted monomeric vinyl chloride left over from the manufacturing process, or hazardous components from plasticizers—which tend to leach out especially when exposed to high temperatures or oils. If these substances inadvertently enter the body, they significantly increase the risk of cancer.

Therefore, use plastic bags labeled "03" with caution when packaging breakfast items such as youtiao, doufunao, and jianbing guozi.

“04” has limited heat resistance—beyond 110°C, it will begin to melt.

"04" That is LDPE (low-density polyethylene).

The common phenomenon of using plastic wrap often results in plastic compounds that the human body cannot break down, and once ingested with food, these substances may even increase the risk of cancer. Moreover, if the food wrapped in plastic is heated—especially when the wrap is on the outside—the fats in the food can more easily dissolve harmful chemicals from the plastic into the food itself.

So, never heat food wrapped in plastic wrap.

“05” is microwave-safe and can be reused after cleaning.

"05" Represents PP (polypropylene).

These items have a wide range of uses, including microwave-safe food containers (such as保鲜盒 and plastic takeout boxes), soy milk bottles, yogurt jars, juice bottles, water cups, straws, and more. Material category 05 is the only one that can be safely heated in a microwave oven, as it withstands high temperatures up to 130°C and has a melting point as high as 167°C.

So products made from this type of material can be reused after proper cleaning and are microwave-safe. However, always exercise caution with unmarked food containers—especially those where the container body is labeled as 05 plastic, but the lid is classified as 06. These should never be heated together in the microwave.

“06” cannot be placed in the microwave and should not be used to hold strong acids or strongly alkaline substances.

“06” That is PS (polystyrene).

Commonly seen items like bowl-shaped instant noodle containers, foam fast-food boxes, and self-service trays are made from this material. While products in Class 06 are both heat-resistant and cold-resistant, they can break down into polystyrene—a carcinogenic substance harmful to human health—when used to hold high-temperature foods or substances that are strongly acidic or alkaline.

Therefore, avoid heating instant noodle containers in the microwave and refrain from reusing them to hold strongly acidic or alkaline substances.

"07," when used properly, can help avoid "Bisphenol A."

"07" Representing PC and other plastics, including polyester, polyamide, polycarbonate, and more.

This is a versatile material widely used in items such as water bottles, mineral water containers, and baby bottles—but it has also sparked considerable controversy due to its content of the toxic substance bisphenol A. When using these products, always choose the appropriate type of plastic based on the specific material and intended use, and follow the instructions and safety guidelines carefully to ensure both safety and reliability.