Plastic bottles are a common part of daily life, and refilling disposable bottles is a simple way to reduce waste. However, whether a plastic bottle remains safe for repeated use depends entirely on the type of plastic and how it is treated. To make an informed choice about reuse, consumers must understand the small number found inside a triangular symbol on the bottle’s bottom. This symbol, known as the Resin Identification Code (RIC), is the key to identifying the raw material used to manufacture the container. Understanding this code is important because different plastic polymers have varying levels of durability and chemical stability when subjected to repeated use, cleaning, and temperature changes.
Decoding the Plastic Numbers
The Resin Identification Code is a standardized system that uses numbers one through seven to classify the type of plastic polymer used in a product. This code was originally developed to help recycling facilities sort materials efficiently, not to indicate the safety of reuse. The number within the triangle identifies the specific chemical composition of the plastic material.
For example, a bottle marked with a “1” is Polyethylene Terephthalate (PET or PETE), typically used for most single-use water and soda bottles. The number “2” identifies High-Density Polyethylene (HDPE), often found in opaque milk jugs and detergent containers. Polypropylene (PP) is represented by the number “5,” commonly used for yogurt cups and some durable reusable containers.
The remaining codes identify other polymers:
- 3 is Polyvinyl Chloride (PVC).
- 4 is Low-Density Polyethylene (LDPE).
- 6 is Polystyrene (PS).
- 7 is a catch-all category for all other types of plastics or multi-material combinations.
Checking this code provides the foundational knowledge needed to assess the container’s suitability for long-term use.
Assessing Safety for Repeated Reuse
The suitability of a plastic bottle for repeated use is determined by the material’s chemical stability and resistance to physical wear. Plastics labeled with the number 2 (HDPE) and number 5 (PP) are the most appropriate for consistent reuse. High-Density Polyethylene (#2) is known for its strength, chemical resistance, and durability against physical stress. Polypropylene (#5) is valued for its high melting point and durability, allowing it to withstand cleaning and repeated handling effectively.
Plastics marked with a number 1 (PET or PETE) should be approached with caution, as they are designed for single-use applications. While safe initially, the thinner PET material is prone to developing micro-scratches and surface degradation upon repeated washing and handling. This wear creates havens for bacterial growth and may increase the potential for chemical compounds, such as antimony, to migrate into the water, especially when exposed to heat.
It is recommended to avoid reusing bottles made from code 3 (PVC), 6 (PS), and those under code 7 (Other). PVC (#3) can contain plasticizers like phthalates, which may leach out. The number 7 category is a mix, but historically included polycarbonate plastics known to contain Bisphenol A (BPA), a compound that can migrate into liquids. Even though many modern #7 plastics are “BPA-free,” the lack of specific material identification makes it difficult to assess the risk of other potentially leachable chemicals.
Maintaining Reusable Plastic Bottles
Bottles made from durable polymers, such as HDPE (#2) and PP (#5), still require careful maintenance to ensure continued safety. The buildup of bacteria is a primary concern, as microbes accumulate in areas like the bottle neck, threads, and surface scratches. Regular, thorough cleaning is necessary to mitigate this microbial risk.
To clean a bottle effectively, wash it with warm, soapy water after every use, preferably using a bottle brush to reach all interior surfaces. It is important to avoid using harsh abrasive cleaners or scouring pads, as these create microscopic scratches in the plastic. These scratches compromise the polymer’s surface integrity, creating sites for bacteria to colonize and accelerating material degradation.
Temperature Sensitivity
Temperature sensitivity is another consideration, as heat rapidly accelerates the breakdown of plastic polymers and increases chemical migration. Avoid exposure to high temperatures, such as placing bottles in a dishwasher, leaving them in a hot car, or filling them with boiling liquids. Studies show that the leaching of compounds like Bisphenol A and antimony increases significantly when temperatures exceed approximately 45–50°C.
Inspection and Retirement
Consumers should regularly inspect reusable bottles for signs of physical deterioration, such as cloudiness, cracking, or deep scratches. Any bottle showing visible wear should be retired from use, as compromised material integrity increases both bacterial and chemical risk.