2026-10-26
Plastic bottles are among the most widely used containers in modern industry, and identifying the resin behind each one has become a routine part of safe household practice. Since industrial production began in 1947, their light weight, durability and low cost have made them the default vessel for storing both liquids and solids. Yet the seven resin categories differ sharply in heat tolerance, chemical stability and recyclability, and those differences carry practical consequences.
Most plastic bottles carry a number from 1 to 7 stamped on the base. The figure identifies the resin family used in manufacturing, which in turn determines the container's physical properties and the conditions under which it can safely be used.
The codes are standardized, but they are not a ranking of safety or quality. Each material was developed for a particular purpose, and a resin suited to detergent packaging may be poorly suited to drinking water.
| Code | Resin | Properties and typical uses |
|---|---|---|
| 01 | PET / PETE | Commonly used for water and beverage bottles. Poor heat resistance; deforms when heated and may release harmful substances. Intended for single use. |
| 02 | HDPE | Frequently used for cleaning and bath product bottles. Relatively good heat resistance, but not recommended as a daily drinking vessel. |
| 03 | PVC | Low heat resistance. Not suitable for holding food or beverages. |
| 04 | LDPE | Found in squeeze bottles. Moderate heat resistance; mainly used in industrial or specialized packaging. |
| 05 | PP | High heat resistance, up to about 130°C. Used for yogurt, condiment and medicine bottles. |
| 06 | PS | Commonly used for disposable cups. Resists neither strong acids nor strong alkalis; unsuitable for orange juice and similar products. |
| 07 | Other | Includes a range of composite materials, some containing endocrine-disrupting substances such as bisphenol A. Requires cautious handling. |
Understanding what a material cannot do is the starting point for protecting health. PET bottles, for instance, may generate carcinogenic compounds after repeated use or prolonged storage, which makes "drink and discard" the safest approach for that resin.
HDPE (code 02) and PP (code 05) are in theory reusable. In practice, however, the complex geometry of bottle bodies makes thorough cleaning difficult, and residual moisture encourages bacterial growth. Long-term reuse therefore carries a hygiene risk even when the plastic itself is stable.
Heat remains the most common source of trouble. Most plastic bottles, and PET in particular, deform physically at high temperatures, a process that can allow chemical components from the material to leach into the contents.
Plastic recovery is governed by strict criteria, and collection systems vary by jurisdiction. In Hong Kong, the official recycling network principally accepts PET (code 01) and HDPE (code 02) bottles, the two streams for which local processing capacity exists.
Items bearing codes 03 through 07 generally fall outside standard collection because their processing is more complex. These are typically channeled through specialist environmental organizations or designated drop-off points, where they can be sorted and handled in a way that limits environmental contamination.
