Not all plastics are made the same way. Manufacturers use different types of plastic materials and compounds, each with unique characteristics.

Explaining plastics could be the subject of a complete online course; therefore, in this article, we just outline a few basic concepts and some of the most popular and widely used types of plastics.

Quick Summary:

• Plastics are broadly categorized into Thermoplastics (meltable/recyclable) and Thermosets (permanent).
• Plastics are categorized globally by 7 Types of Plastic or Resin Identification Codes (RICs): #1 PET, #2 HDPE, #3 PVC, #4 LDPE, #5 PP, #6 PS, and #7 Other (Polycarbonate, BPA, Bioplastics).

Why Writing an Article about Plastic on a Platform that Promotes “Plastic-free”?

Some products contain plastic materials or components that are less well recognised by many of us, so it’s important to have some knowledge about the different types of plastic. This guide might be helpful for you to better understand how much plastic is around, how to avoid it to fight plastic pollution, and how to protect your health from endocrine disruptors like Bisphenol A (BPA) (1) and phthalates (2). Knowing which resins leach more harmful additive chemicals also empowers you to make safer choices for your home or organisation. Last but not least, it helps your recycling efforts, when plastic cannot be avoided, and helps reduce your microplastic exposure.

What is “Plastic”? How is Plastic Made?

Plastic is made with hydrocarbons from fossil fuels such as crude oil and natural gas, along with materials like coal, salt and plant-based cellulose. These raw materials are processed into small chemical building blocks called monomers. Through a chemical process called polymerisation, the monomers join together to form long chains known as polymers, creating the versatile material that can be shaped into countless products.

Where Does the Word “Plastic” Come From?

• Ancient origins: The word comes from the Greek verb plassein, meaning “to mold” or “to form”, much like shaping clay.
• Early use: The term entered the English language in the 1600s, originally describing materials that were soft, pliable or easy to shape, such as clay and wax.
• Modern meaning: It wasn’t until the early 20th century that “plastic” became associated with the synthetic materials we know today. The name stuck because these materials can be softened, molded and formed into virtually any shape.

Who Invented Plastic?

The first fully synthetic plastic, Bakelite, was developed in 1907 by Belgian-American chemist Leo Baekeland (3). However, the history of plastics began earlier, with inventors such as Alexander Parkes and John Wesley Hyatt developing early man-made and semi-synthetic materials.

Early milestones in plastic history

• 1856: Alexander Parkes developed Parkesine, an early man-made plastic made from cellulose.
• 1869: John Wesley Hyatt developed celluloid, originally created as an alternative to ivory for products such as billiard balls.
• 1907: Leo Baekeland created Bakelite, widely recognised as the first fully synthetic plastic and the first plastic capable of withstanding high temperatures.

Thermoplastics versus Thermosets

Plastics are mainly classified by their thermal behaviour into thermoplastics & thermosets.

1. Thermoplastics

Thermoplastics melt and can be reshaped when heated, then harden when cooled; they can be recycled multiple times (e.g., polyethylene (PE), polypropylene (PP), or polyvinyl chloride (PVC).

2. Thermosets

Thermosets set permanently, forming permanent chemical bonds during curing; they decompose rather than melt when reheated (e.g., epoxies, silicone, vulcanised rubber).

Related: What is Chemical Recycling and Why It Is not the Ultimate Solution to Plastic Pollution

7 Resin Identification Codes (RIC) also called
7 Plastic Identification Codes (PIC)

These seven symbols are known as Plastic Resin Identification Codes (RICs) or Plastic Identification Codes (PIC) and in the USA are managed by the ASTM International (4). Introduced in 1988 by the Plastics Industry Association, their purpose was simply to identify the type of plastic used in a product.

1. Polyethylene terephthalate (PET / PETE)

PET or PETE is the acronym for polyethylene terephthalate, the chemical name for polyester. PET is a clear, strong, and lightweight plastic that is widely used for packaging foods and beverages, especially convenience-sized soft drinks, juices and water. Virtually all single-serving and 2-liter bottles of carbonated soft drinks and water sold in the U.S. are made from PET.

Polyethylene terephthalate has excellent chemical resistance to water and is easily recyclable. This plastic has a higher strength than its weight, and it is used in the production of fibers for clothing, food containers and liquids, glass fibers for engineering resins, carbon nanotubes, and many other products.

PET / PETE Plastic Applications:

• Drink bottles (soda, mineral water, etc.)
• Synthetic clothing
• Fruit storage boxes
• Insulation of walls
• Microwave trays

2 . High-Density Polyethylene (HDPE):

Polyethylene is the most common plastic on earth and is manufactured in various densities. Each different density of polyethylene gives certain characteristics to the final plastic. As a result, polyethylene is a highly versatile product.

The three common density categories of polyethylene (PE) are:

1. LDPE — Low-Density Polyethylene:
   Flexible and soft. Common in plastic bags, films, and squeeze bottles.
2. MDPE — Medium-Density Polyethylene:
   A balance between flexibility and strength. Used in pipes, packaging and some containers.
3. HDPE — High-Density Polyethylene:
   More rigid and durable. Common in plastic milk bottles, detergent bottles, water and sewage pipes, snowboards, boats, folding chairs, and sturdy containers.

In simple terms: the higher the density, the more rigid and less flexible the polyethylene tends to be.

HDPE Plastic Applications:

• Plastic milk bottles
• detergent bottles
• water and sewage pipes
• snowboards, boats,
• sturdy containers.

3 . Polyvinyl Chloride (PVC)

Polyvinyl Chloride (PVC) is a synthetic plastic polymer that is widely manufactured because of its rigid and flexible properties. This plastic is well known for its ability to blend in with other materials. Large PVC sheets, for example, are made of polyvinyl chloride foam, which is used to make custom products such as kiosks, product displays in shops, and exhibitions. PVC solid form is commonly used in building materials, doors, windows, bottles, food packaging, and so on. Adding plastic-associated chemicals (PACs) such as phthalates makes this plastic type softer and more flexible.

PVC Plastic Applications:

• U-PVC (unplasticized polyvinyl chloride), also called PVC-U pipes, used in water and wastewater
• Electric cables (cable insulation)
• Packaging drugs, especially tablets
• Steel rope cover
• Garden hoses, plastic slippers
• Boats and sailing boats
• Use as flooring for buildings
• Different uses in apparel (clothing)

4. Low-Density Polyethylene (LDPE):

LDPE (Low-Density Polyethylene) is a soft, flexible, and moisture-resistant thermoplastic widely used across industries for products requiring high ductility, impact strength, and chemical resistance. It’s used to produce soft-plastic products such as shopping bags, plastic bags, light food containers, disposable packaging, and so on.

LDPE Plastic Applications:

• Plastic films and sheets: Grocery bags, bread bags, shrink wrap, and stretch wrap.
• Medical: Flexible medical tubing and intravenous (IV) bags, Disposable medical gloves and protective aprons
• Squeezable condiment bottles (mustard, honey, sauce)
• Flexible plastic squeeze tubes (lotions, ointments)
• Soft-touch plastic children’s toys

5. Polypropylene (PP)

It is an elastic polymer and the second-largest synthetic plastic produced in the world. The reason for its widespread use and popularity is that propylene is undoubtedly the most flexible synthetic plastic on the planet. Although propylene is stronger than polyethylene, it still retains its flexibility. This plastic does not crack due to constant pressure. Due to its heat resistance, flexibility, stability, acid resistance, and cheapness, propylene sheets are used for manufacturing laboratory equipment, auto parts, medical supplies, and food containers.

PP Plastic Applications:

• Ropes looms, and knitting yarns
• Food containers such as yogurt, sauces, etc.
• Medicinal containers and bottles and even baby’s milk glass
• Gasoline tank, chemical tank
• Different luggage structures
• Covering different batteries

6. Polystyrene

Polystyrene is a versatile plastic used to make a wide variety of consumer products. As a hard, solid plastic, it is often used in products that require clarity, such as food packaging and laboratory ware. When combined with various colorants, additives, or other plastics, polystyrene is used to make appliances, electronics, automobile parts, toys, gardening pots and equipment and protective packaging (such as packing peanuts (5) and CD and DVD cases), containers, lids, bottles, trays, tumblers, disposable cutlery and in the making of models.

Polystyrene is not to be confused with Expanded PolyStyrene (EPS) which is a lightweight, foamed form of polystyrene made by expanding small plastic beads with steam inside a mould. EPS is a type of polystyrene.

Polystyrene Plastic Applications:

• Disposable cups, plates, and bowls
• Yogurt containers and egg cartons (not the cardboard ones!)
• CD and cassette cases
• Electronics housings: Cases and internal parts for TVs, computers, and audio equipment.
• Protective shipping foam and packing peanuts (EPS)

 7. Other (Polycarbonate, BPA, and Bio-Based Plastics)

Code 7 is a catch-all category for any plastic resin that doesn’t fit into codes 1 through 6, as well as products made from a combination of different plastics. Historically, this code primarily represented Polycarbonate (PC) a hard, clear plastic infamous for leaching Bisphenol A (BPA) and BPS.

Over time, especially when heated or exposed to harsh detergents, these chemical bonds break down and leach BPA into food and liquids. Concerns over endocrine disruption led to strict FDA regulations on BPA in baby bottles and packaging (1), banning its use in baby bottles, sippy cups, and infant formula packaging.

Today, while many manufacturers have switched to BPA-free alternatives like Tritan™ or Polypropylene (Code #5), older or imported items marked with a #7 may still contain polycarbonate.

Furthermore, Code 7 also includes modern bio-based plastics like Polylactic Acid (PLA) (derived from corn starch or sugarcane), as well as Acrylic, Fiberglass, and Nylon. Found in everything from baby bottles and reusable water jugs to eyeglasses and bioplastic food packaging, #7 plastics are almost never accepted in standard curbside recycling programs and represent the highest potential risk for chemical leaching among consumer packaging.

Plastic Applications:

• PLA biodegradable plastic cups & food packaging
• Polycarbonate (PC): baby bottles, office water jugs
• Tritan™ (Copolyester): newer baby bottles, reusable sports water bottles

Related: 7 Creative Ways to Embrace Biodegradable Alternatives to Plastic that Make a Difference

Liquid Polymers vs. Microplastics: The Regulatory Loophole

While microplastics are widely discussed, liquid synthetic polymers in cosmetics and detergents present a major regulatory loophole. How ECHA Defines Microplastics:

Under EU REACH (Annex XVII, Entry 78) (6), the European Chemicals Agency (ECHA) legally defines microplastics as Synthetic Polymer Microparticles (SPMs), specifically synthetic polymers that are solid, insoluble in water, non-biodegradable, and  5mm in size.

The “Liquid Microplastic” Grey Area

Because legal definitions strictly require a solid state, liquid, gel, or water-soluble synthetic polymers, such as dimethicone, carbomer, polyquaternium, or PEGs are excluded from official microplastic bans. These occur particulrly in cosmetics polluting the environment ad ultimately ourselves, as summarised in the report by UNEP (7):

• Environmental Impact: Wastewater plants cannot filter out liquid polymers, allowing them to flow directly into waterways.
• Lack of Biodegradability: Like solid plastics, many liquid polymers are engineered to resist natural degradation.

Common Ingredients to Avoid:

• Silicones: Dimethicone, Cyclopentasiloxane
• Acrylates: Carbomer, Acrylates Copolymer
• Polymers: Polyquaternium, Polyethylene Glycol (PEG)

Related: Microplastics 101: What Are Microplastics & How to Reduce Exposure

FAQ about The Plastic Recycling Codes

– Are The Plastic Identification Codes Recycling Symbols?

The Plastic Identification Codes are not recycling symbols. They do not indicate that an item is recyclable or provide guidance on how it should be disposed of.

The presence of a particular plastic resin does not automatically mean the item can be recycled through kerbside systems. Recyclability depends on factors such as the material composition, product specifications, colour, and the recycling infrastructure available in your local area.

This is a perfect example of why recycling can be so confusing for consumers. When a symbol looks like a recycling symbol but doesn’t actually indicate whether an item is recyclable, it makes it much harder for people to know what belongs in which bin.

– Can Plastic be Liquid?

Liquid polymers, from a strict regulatory and environmental science standpoint, are not considered true microplastics, because microplastics are legally defined as solid, insoluble particles. However, they represent a significant environmental loophole, and they are very common in cosmetics.

The term “liquid microplastics” is an informal catchphrase used by environmental advocacy groups to describe synthetic liquid polymers that are poorly biodegradable. However, from a strict regulatory and environmental science standpoint, they are not considered true microplastics, because microplastics are legally defined as solid, insoluble particles. Therefore, they represent a significant environmental loophole.

Related: Why You Should Switch to Plastic Free Skincare Brands

Final Thoughts

Understanding the 7 types of plastic and their Resin Identification Codes (RIC) is essential for navigating modern materials safely. While plastics like #2 HDPE and #5 PP offer safer, highly recyclable profiles, others such as #3 PVC, #6 PS, and #7 the Polycarbonate type pose notable chemical leaching risks and environmental challenges. By recognizing these resin codes and looking out for hidden synthetic polymers, you and your company can make informed choices to protect human health, simplify recycling, and actively reduce your organisation’s plastic footprint.

References & Scientific Research Studies

(1) U.S. Food and Drug Administration. (2022). Bisphenol A (BPA): Use in food contact applications. U.S. Department of Health and Human Services. https://www.fda.gov/food/food-packaging-other-substances-come-contact-food-information-consumers/bisphenol-bpa-use-food-contact-application

(2) U.S. Food and Drug Administration. (2022). Phthalates in food packaging and food contact applications. U.S. Department of Health and Human Services. https://www.fda.gov/food/food-additives-and-gras-ingredients-information-consumers/phthalates-food-packaging-and-food-contact-applications

(3) Science History Institute. (2016). Leo Hendrik Baekeland. Science History Institute Digital Collections. https://www.sciencehistory.org/education/scientific-biographies/leo-hendrik-baekeland/

(4) ASTM International. (2021). Standard practice for coding plastic manufactured articles for resin identification (ASTM D7611 / D7611M – 21). ASTM International. https://store.astm.org/d7611_d7611m-21.html

(5) Wikipedia. (2023). Foam peanut. Wikimedia Foundation. https://en.wikipedia.org/wiki/Foam_peanut

(6) European Commission. (2019). Study to support the development of potential measures on microplastics. REACH restriction of synthetic polymer microparticles. CircaBC. https://webgate.ec.europa.eu/circabc-ewpp/d/d/workspace/SpacesStore/e094e675-7785-4b92-b030-a91a6bbdae7d/download

(7) United Nations Environment Programme. (2015). Plastics in cosmetics: Are we polluting the environment through our personal care? UNEP. https://www.unep.org/resources/report/plastics-cosmetics-are-we-polluting-environment-through-our-personal-care