What are microplastics?

Microplastics are plastic particles smaller than 5 millimetres in at least one dimension. Some are visible as tiny coloured fragments. Others are too small to see without magnification.

The term describes a size category, not one material. A microplastic can be a fibre, film, fragment, bead, pellet, or piece of foam. It can be made from many different polymers, contain different additives, and range from nearly 5 mm down to the limits of a study’s detection method.

Definition and research overview: U.S. EPA

Close-up of coloured plastic films, fragments, fibres and a foam bead collected in a plankton net — A plankton-net haul from the Mediterranean surface: films, hard fragments, coloured fibres, and a foam bead in one sample. This mix is what a surface trawl actually recovers before anything is counted or identified. François Galgani / Ifremer, Ifremer image library · CC BY 4.0

Microplastics and nanoplastics

Well established

Five millimetres is roughly the width of a pencil eraser. A human hair is approximately 70–80 micrometres wide. Nanoplastics are generally described as smaller than 1 micrometre, although exact definitions are not yet universal.

Smaller particles are much harder to collect and identify. This is one reason particle counts from different studies cannot always be compared or combined.

5 mm

Microplastic upper boundary

70 µm

Approximate human-hair width

1 µm

Common nanoplastic boundary

Circle diameters use a compressed logarithmic-style scale so all three remain visible. The labels give the actual dimensions.

How they begin

Primary microplastics: Particles intentionally manufactured at a small size, including some industrial pellets, powders, and microbeads.
Secondary microplastics: Particles created when larger products shed or break apart. Sources include tires, synthetic textiles, paint, packaging, artificial turf, fishing gear, and discarded plastic.

Pale plastic pellets mixed through dried seaweed and sand along a beach strandline — Nurdles—lentil-sized pellets that plastic is shipped and moulded from—washed into the strandline at Dawlish Warren, Devon. They are primary microplastics: manufactured small, not broken down from something larger. Partonez, Wikimedia Commons · CC BY-SA 4.0

Explore where they come from

The main particle forms

Well established

Fragment

Fibre

Film

Bead

Foam

Shape categories used by researchers; these diagrams are not microscope images and are not to scale.

Four microscope panels showing plastic filaments, fragments and spheres recovered from river sediment, each with a one-millimetre scale bar — Microplastics sieved from the sediment of four European rivers, showing the main forms side by side: filaments, fragments, and spheres. Each white bar is 1 mm. The arrowheads mark particles that are not plastic—aluminium foil in panel C, glass spheres in panel D—which is why researchers confirm polymers instead of sorting by eye. Wagner et al., Environmental Sciences Europe, Microplastics in freshwater ecosystems · CC BY 4.0

Fragments: Irregular pieces created when rigid plastic breaks apart.
Fibres: Thin strands commonly associated with synthetic textiles, ropes, and nets.
Films: Flexible, flat pieces that can come from bags, wraps, and agricultural film.
Beads and pellets: Rounded particles that may be manufactured at a small size.
Foam: Lightweight, porous pieces from expanded plastic products.

Why one particle is not like another

A particle’s behaviour and potential effects depend on more than whether it is plastic.

Gloved hand holding a labeled glass jar with water and collected debris — A field sample contains water, organic matter, minerals, and possible plastics. Separation and identification come next. U.S. Geological Survey, USGS Milwaukee sample jar · Public domain

Size: Particles near 5 mm behave differently from particles measured in micrometres or nanometres.
Shape: A fibre, film, and fragment move through air, water, and organisms differently.
Polymer: Polyethylene, polypropylene, polyester, nylon, and other plastics have different densities and properties.
Chemicals: Plastics may contain additives and can interact with chemicals or microorganisms in their surroundings.
Weathering: Sunlight, heat, friction, and waves can change a particle and break it into smaller pieces.

Continue learning

Read the six-part sequence in order, or jump to a topic.

Where they come fromTires, textiles, paint, packaging, turf, pellets, and litter.Food, water, and airWhat studies report and why concentration estimates vary.Wildlife and ecosystemsIngestion, food webs, aquatic life, soil organisms, and plants.Microplastics and the human bodyExposure routes, reported findings, and limits of health evidence.Why global comparisons are hardA small set of measured values and the method limits behind them.Resources and sourcesOfficial explainers, reviews, datasets, and primary research.