Have you noticed that many plastic containers or bottles have three arrows printed on the bottom, with different numbers (usually 1 through 7) inside them?

These symbols are used to identify the type of plastic resin used in these products. Different types of plastic are used for various types of packaging, such as soda bottles, laundry detergent bottles, and food containers. Strictly speaking, these resin identification codes were introduced by the Society of the Plastics Industry (now the Plastics Industry Association) in 1988 to help identify plastic materials and facilitate sorting for recycling. However, these codes do not guarantee that a product is recyclable or accepted by local recycling programs.

The numbers represent the following:

1. Polyethylene Terephthalate (PET or PETE)
Commonly used for bottled water, soft drinks, cooking oil, peanut butter jars, and other food containers

2. High-Density Polyethylene (HDPE)
Commonly used for laundry detergent bottles, milk and juice containers, shampoo bottles, and some plastic bags

3. Polyvinyl Chloride (PVC), also known as vinyl
Used in products such as medical tubing, electrical wire insulation, plastic flooring, and certain packaging

4. Low-Density Polyethylene (LDPE)
Commonly used for bread bags, shopping bags, plastic films, trash bags, and squeezable bottles

5. Polypropylene (PP)
Commonly used for medicine bottles, yogurt cups, food containers, bottle caps, and some beverage bottles

6. Polystyrene (PS)
Commonly used for disposable plastic cups, plates, cutlery, food trays, and foam packaging

7. Other plastics or mixed materials
Includes plastics not covered by codes 1–6, such as polycarbonate, ABS, acrylic, nylon, and certain multilayer or mixed-material products. Examples may include some large water bottles, specialized food containers, and other durable plastic products

You may be surprised to learn why so many different codes are used to distinguish plastic resin types, but this information can help explain the properties and characteristics of plastics. Different plastics are suited to different applications: some make products squeezable, such as mustard bottles, while others provide strength and durability for products such as pipes and protective panels. Furthermore, resin identification codes provide useful information for sorting plastics and supporting recycling and environmental sustainability. However, whether a plastic product can actually be recycled depends on its material composition, local collection programs, and available recycling facilities.

作者：Michael Chiu，MWS，CI
本文原載於《明報》－2026年更新修訂