Understanding the Plastic Codes Printed on Everyday Containers

The small triangle stamped on the bottom of plastic containers carries one of the most useful pieces of consumer information in your home, and almost nobody reads it. The number inside the triangle is not a recycling priority, it is a resin code. Each number identifies a specific plastic family, with different properties, safety profiles, and lifespans.

Knowing how to read these codes changes the experience of shopping for food storage, water bottles, baby products, and almost any rigid container. It also explains why some plastic items survive a hundred dishwasher cycles while others crack on the third.

Code 1: PET, the bottle plastic

PET, or polyethylene terephthalate, is the clear, lightweight plastic used for most single-use water bottles, soft drink bottles, and salad clamshells. It is recyclable in most municipal systems and is safe for single use, but it is not designed for reuse. The surface is microporous and develops scratches that hold bacteria.

If a bottle says it is made of PET and the label does not explicitly say it is safe for refilling, treat it as single use. Refilled PET bottles can leach trace plasticisers over time, especially in warm conditions.

Code 2: HDPE, the milk jug

HDPE, or high density polyethylene, is the opaque, slightly waxy plastic used for milk jugs, shampoo bottles, and some food storage. It is one of the safer plastics in everyday use, tolerates a range of temperatures, and is widely recyclable.

HDPE containers are durable and can be washed and reused without significant degradation. Many premium food storage containers are made of HDPE, particularly those designed for freezer use. A jug stamped with the number 2 is generally a safe bet for refillable use.

Code 3: PVC, the one to read twice

PVC, or polyvinyl chloride, appears in cling film, plumbing pipes, and some toy or accessory products. It is the most chemically complex of the everyday plastics. Modern food-contact PVC is regulated and considered safe for its intended use, but PVC is rarely the best choice for food storage, and its recycling stream is limited.

If a container is stamped 3 and is meant for food storage, look for alternatives. The performance and safety of better plastics in the same role is usually higher.

Code 4: LDPE, the bag plastic

LDPE, or low density polyethylene, is the soft, stretchy plastic used for grocery bags, bread bags, and squeeze bottles. It is flexible, low-cost, and food safe in its standard use. LDPE recycling is improving but remains less common than HDPE recycling.

Most cling-style food wraps marked safer than PVC are made from LDPE or LLDPE. They cling less aggressively but are simpler in composition.

Code 5: PP, the workhorse for warm food

PP, or polypropylene, is one of the most useful everyday plastics. It is heat tolerant up to roughly 120 degrees Celsius, microwave safe in most forms, and resistant to fatigue. Yogurt tubs, microwave dishes, and reusable food containers are commonly PP.

If you reheat food in plastic containers, PP is the resin you want. Containers stamped 5 hold their shape under heat and do not warp the way some of the lower-numbered plastics do.

Code 6: PS, including foam

PS, or polystyrene, comes in both rigid and foam forms. Rigid PS appears in disposable cutlery and clear takeout containers. Foam PS is the white styrofoam familiar from packaging and old-style coffee cups. PS recycling is rare and the material is brittle.

For everyday use, PS is acceptable as single use packaging but a poor choice for reusable storage. Better options exist at similar price points.

Code 7: Other, including bioplastics

Code 7 is a catchall that covers everything not described by codes 1 through 6. This includes polycarbonate, certain bioplastics made from corn starch, and various blends. Some are entirely safe and modern, others are older formulations that should be replaced.

A 7 by itself does not tell you what the plastic is. The text below the triangle usually clarifies. Look for the words PC, BPA-free, or PLA. Older PC products without the BPA-free designation are worth retiring.

Closing thoughts

The triangle on the bottom of a plastic container is one of the most useful labels in everyday consumer goods, and it takes ten seconds to learn how to read it. Once you do, the shelf becomes legible in a way it was not before.

The codes do not tell you which product is best for you, but they make it easier to know what you are paying for. That alone changes the experience of shopping for storage, drinks, and toys for the rest of your life.

Heat tolerance and typical uses by resin

Every resin has a temperature range beyond which it softens, deforms, or begins to release volatiles. The values below are typical maxima for continuous food contact use.

Reading a container at a busy shelf

1. Turn the container over and locate the small triangle. On soft films the code often sits near the seam on a corner.
2. Read the number inside. The letters below the triangle (PET, HDPE, PP) confirm the resin family.
3. For code 7, check for the abbreviation PC, PLA, or the phrase BPA-free. Older PC without a BPA-free note can leach bisphenol A, especially after exposure to hot water.
4. Check the base and rim for a fine seam. A ridged, hazy seam near a code 1 stamp suggests a bottle intended for a single fill.
5. Look at the interior surface. Fine white scratches on a resin marked 1 mean the microporous surface has begun to hold residue and the bottle is past its useful life.

Retirement signs for a container in daily use

• Cloudy or hazy interior on a formerly clear bottle: surface degradation from repeated dishwasher cycles.
• Warping or bowl-out after microwave use: the resin has passed its glass transition point.
• Sticky or tacky patches on a lid: plasticiser migration, common in older PVC.
• Persistent food odour after washing: micro-cracks holding residue, a sign the plastic has aged.
• Visible cracks radiating from the rim: stress crazing, particularly common in PS and low-grade PET.

For a fuller overview of the resins and the chemistry that shaped modern polycarbonate labelling, the Wikipedia entry on bisphenol A covers the regulatory history. Related material guides include stainless steel grades for food storage, glass types in the kitchen, and nonstick coating chemistry.