The best-known toy brick maker is the LEGO company, which is based in Billund, Denmark (as of November 2026). Its name comes from two Danish words, leg godt, which mean play well, and the word lego also means 'I put together' in Latin, a coincidence the company noticed later. Yet the idea of an interlocking plastic brick had another source. Kiddicraft, a British company, had sold interlocking plastic bricks with studs before LEGO did. Hilary Page, who founded Kiddicraft in 1932, had patented hollow interlocking plastic bricks with 4 and 8 studs, and the V&A says he patented the brick in 1939. The Christiansens came across Kiddicraft prototypes in 1947 and made their own version two years later.

Page chose plastic because paint on wooden toys could be sucked or chewed off, and plastic was hygienic and had no sharp edges. Plastic production took off after World War II, in the 1950s, and plastic was chosen for toys partly because it is easy to clean and comes in many colors and shapes. LEGO acquired a plastic injection-molding machine in 1947, the first in Denmark. Sales of the plastic toys were nevertheless mediocre in the early 1950s. In 1958 the bricks were hollow underneath, so models were wobbly and customers complained, and Godtfred Kirk Christiansen sketched several fixes, including tubes, at a meeting on January 23, 1958. The patent for the brick was filed on January 28, 1958, and it covered a system of interlocking bricks, not only the studs and tubes.

Toy bricks stick together because the studs on top fit tightly between the tubes inside another brick. A brick one stud wide has no room for a tube, so it has a thin bar that the studs squeeze slightly. The plain hollow Kiddicraft-style brick gripped less well, while later LEGO bricks added tubes underneath, which gave the studs more points of contact and stiffened the brick against warping. The 1958 tube design is credited with turning sales around. The pull needed to separate two bricks has a name: clutch power is the force needed to pull two bricks apart, it is measured in newtons, and LEGO keeps the exact ideal number secret. With the stud-and-tube design, six 2x4 bricks can be combined in 915,103,765 different ways, according to LEGO.

The material is as carefully chosen as the shape. ABS is a mix of three ingredients, acrylonitrile, butadiene and styrene. Polybutadiene, a rubbery substance, is the part that provides toughness, and makers use it as an additive to improve the impact resistance of plastics that are otherwise more brittle. For most uses ABS works between -20 and 80 degrees C, because its mechanical properties change with temperature. As a strong material that can survive being dropped, it is used for objects that take knocks, such as cameras, phones and computer cases. LEGO changed from the wood-based cellulose acetate to ABS in 1963 because ABS was more stable and held color better.

ABS is also a thermoplastic. It is an amorphous solid, which means it has no definite melting point, because its monomer chains vary in length and are cross-linked to different degrees, and its glass transition temperature is about 105 degrees C. Thermoplastics suit injection molding because they can be recycled, are versatile and soften and flow when heated. By contrast, a thermoset left in the barrel too long cross-links and can seize the screw and check valves. At LEGO the ABS is heated to 232 degrees C (450 degrees F) until it is dough-like and injected into the molds with forces of between 25 and 150 tonnes.

Hot plastic spreads through little channels and fills the brick-shaped space in the mold. Cold water flows through the mold to cool the plastic, after which the mold opens and the bricks drop onto a belt. ABS is cheap, takes any color and can have a glossy finish, and color is added at the machine, so one plastic can make bricks of many colors. In the Billund factory a full collection bin under a molding machine signals a robot, which drives down the aisle on its own and leaves an empty bin so production resumes. Eight robots moved 600 bins per hour, according to a 2016 report.

Molds are the most guarded secret of the factory, and a 2011 report said the average mold was worth $72,000 and the most valuable about $360,000. In 2011 a single big factory module in Billund had up to 64 molding machines in two aisles of 32, and a big plant could make more than two million pieces every hour in 2008. The plastic itself waits in silos. A 2016 report said an average plant has about 14 silos, each holding 33 tons, and at Billund in 2008 the silos fed the molding lines about 60 tons of granules every 24 hours. The main warehouse holding the silos was half a kilometer long.

After molding, machines assemble pieces made of several parts by applying precise amounts of pressure. A small robot adds hands to a minifigure, and a machine stamps on printed details such as a face and a shirt. Decorating, such as painting faces and patterns, is the most expensive part of making a LEGO piece. Pieces for sets are put into small bags, and the bags go into boxes that machines close. Quality is checked by weight: in 2011 a factory tour found that a pre-pack bag had to weigh between 94.9 and 95.7 grams, and a display showed 5,354 bags in range and six out. Scales that notice a difference of a few micrograms set off an alarm so an operator can re-sort the box.

Waste is the other side of the factory. Plastic left in the channels falls down the machine, is ground up and goes back into the production cycle. In 2011 a visit found that almost all the plastic in a LEGO factory was reused, and a 2008 report said LEGO recycles all but about 1 percent of its manufacturing plastic waste. What cannot go back into bricks, such as faulty pieces and the clear plastic used to flush a machine between colors, is ground up and sold to other industries, which in 2008 made pipes and even heating oil from it.

A thrown-away toy is a different story. ABS can be recycled, but it is not accepted by all recycling facilities, and in the UK councils do not take it in household recycling. Plastic that is thrown away does not rot away like food or paper, and it can stay around for hundreds of years. Plastic made in the world grew from about two million tonnes in 1950 to more than 400 million tonnes a year today (2026). Estimates of how much plastic enters the oceans have changed: earlier work said up to 8 million tonnes a year, while recent high-quality studies suggest 1 to 2 million tonnes, which shows how hard it is to measure.

Much plastic waste comes from places with weak trash collection, so how trash is handled matters as much as how much there is.

LEGO said in 2023 that it would cut carbon emissions 37 percent by 2032. It dropped a recycled-bottle brick prototype after two years of testing, because it would not have cut carbon emissions. It is also moving its brick packing lines away from single-use plastic bags: it announced in 2020 that it would use recyclable paper bags, and 56 percent of the lines have now switched (as of November 2026).

Bricks are built to be taken apart and built again, and new bricks still fit bricks made since 1958.

Words to know

• amorphous: without fixed shape
• thermoplastic: plastic that melts
• prototypes: first test models
• polybutadiene: rubbery ingredient
• silos: storage tanks