The best-known toy brick maker is the LEGO company, which is based in Billund, Denmark (as of November 2026), and its name comes from two Danish words, leg godt, which mean play well. Yet the brick has a disputed ancestry. Hilary Page, an English toy designer, patented hollow interlocking plastic bricks with 4 and 8 studs; he founded his company Kiddicraft in 1932, and the V&A says he patented the brick in 1939. A 1944 addition, granted in 1947, described a system of rectangular hollow blocks with 2x4 studs that allowed walls with staggered rows and window openings. The Christiansens came across Kiddicraft prototypes in 1947 and made their own version two years later.
Histories disagree about when LEGO got the rights to Kiddicraft's design: the V&A museum says 1949, while Grace's Guide says LEGO acquired his intellectual property in the 1980s. In 1981 LEGO settled out of court with Hilary Page's estate, reportedly for about £45,000, to keep using the brick design, and the Kiddicraft trademark was not part of the deal and was later sold separately to Fisher-Price.
Sales of LEGO's plastic toys had been mediocre in the early 1950s, and many shipments were returned. In 1958 the bricks were hollow underneath, so models were wobbly and customers complained. Godtfred Kirk Christiansen sketched several fixes, including tubes, at a meeting on January 23, 1958, and the patent was filed five days later. It covered a system of interlocking bricks, not only the studs and tubes, and the application included a hand-glued 2x4 mock-up. When the first 2x4 bricks with tubes were made, the stud-and-tube pair was invented. The 1958 tube design is credited with turning this around.
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, and later LEGO bricks added tubes underneath, which gave the studs more points of contact and stiffened the brick against warping. Clutch power is the force needed to pull two bricks apart; it is measured in newtons, and LEGO keeps the exact ideal number secret. LEGO has not changed the brick's basic connection since 1958, so a new brick still fits an old one, and with the stud-and-tube design, six 2x4 bricks can be combined in 915,103,765 different ways, according to LEGO.
The plastic has its own chemistry. ABS is a mix of three ingredients, acrylonitrile, butadiene and styrene. It is styrene-acrylonitrile (SAN) plastic made tough by polymerizing it in the presence of rubbery polybutadiene, which leaves a long polybutadiene chain crisscrossed with shorter SAN chains. Each ingredient has a job: acrylonitrile adds chemical resistance, hardness and rigidity; styrene gives a shiny surface and easier processing; polybutadiene adds toughness. Changing the proportions makes different grades, such as grades for extrusion or for injection molding.
LEGO switched from cellulose acetate, which is based on wood, to ABS in 1963 after a series of tests. ABS was more stable and color-fast, and the better material allowed greater precision in molding, which the company's history gives as an accuracy of 1/200 mm. Numbers for mold precision are not the same everywhere, however. A 2016 trade report quoted a tolerance, the amount a part's size is allowed to be off, of as little as 0.002 mm, so the figures should be read as rough and dated. Raw ABS is naturally translucent ivory to white, so pigments are added to color it. At LEGO the color for specific bricks is added at the molding machine, so one stock of granules can make every color. The later ABS bricks keep their shape, being less prone to warping. ABS is cheap, takes any color and can have a glossy finish, and plastic was chosen for toys partly because it is easy to clean and comes in many colors and shapes.
In a molding machine, pelletized plastic drops from a hopper into a heated barrel with a reciprocating screw. The screw mixes and homogenizes the melt and, by mechanically shearing the plastic, adds frictional heat that shortens the heating time needed. 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. Thermoplastics suit this process because they can be recycled, are versatile and soften and flow when heated, while a thermoset left in the barrel too long cross-links and can seize the screw and check valves.
Plastic enters a mold through a sprue or gate and flows along channels called runners to the cavities. Cooling decides much of the cycle time. Once the gate has frozen, the part cools in the mold, and cooling lines circulating water or oil from an external temperature controller cut this time sharply. Then the mold opens and pins, sleeves or strippers push the part out. Sources disagree on how long a brick takes: one 2016 report says the new pieces cool and fall onto a conveyor after about seven seconds, while Wikipedia, citing a 2008 source, says the plastic takes approximately 15 seconds to cool.
The mold itself is a piece of engineering. A mold can have one cavity or many; in a multi-cavity mold every cavity may make the same part or different parts in one cycle. Molds are generally tool steel, because injection molds need steels that resist abrasion to last hundreds of thousands of molding operations. At LEGO they 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.
A single big factory module in Billund had up to 64 molding machines in two aisles of 32, and there were 12 such modules in 2011. When a collection bin under a molding machine fills, the machine signals a robot, which drives down the aisle on its own, takes the full box and leaves an empty one so production resumes. In the Billund factory eight robots moved 600 bins per hour, according to a 2016 report. Few people work on the factory floor, because computers and machines handle most of the work.
After the molds, LEGO checks quality in several ways. Human inspectors look at the output of the molds to eliminate significant variations in color or thickness, and about eighteen bricks in every million fail to meet the standard, according to the company. Packing is checked by weight: in 2011 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 (five too light, one too heavy). Scales that notice a difference of a few micrograms set off an alarm so an operator can re-sort the box. LEGO had a quality control department of 13 people by 1963.
How strong is one brick? Engineers at the Open University tested a 2x2 ABS brick in a hydraulic testing machine until it failed. The average brick took about 432 kg (950 lb) before it deformed, and since one brick has a mass of 1.152 g that equals a tower of about 375,000 bricks, roughly 3.5 km high. The brick did not shatter. It failed by plastic deformation, the material flowing out of the way while the brick kept deforming without the load increasing. A real tower would fail long before the bottom brick, because loading would never be perfectly equal or symmetric, so a tiny flaw in the structure would be massively amplified.
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. A thrown-away toy is a different story, because plastic that is thrown away does not rot away like food or paper, and it can stay around for hundreds of years, and 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.
In 2018 the New York Times reported that LEGO's footprint was about a million tons of carbon dioxide a year. By 2023 the company said it had tested more than 300 materials, aiming to cut emissions 37 percent by 2032. A recycled-bottle brick prototype was dropped in 2023 after two years of testing because it would not reduce carbon emissions. LEGO's rise to 52 percent renewable and recycled content in 2025 came mainly from buying more certified materials, not from a new kind of brick (as of March 2026). Most LEGO bricks are made of ABS, an oil-based plastic. The company is also moving its brick packing lines away from single-use plastic bags, which it announced in 2020 when it said it would use recyclable paper bags, and its sustainability pages report that 56 percent of the lines have now switched (as of November 2026).
Many plastic things, such as bottles and takeout boxes, are made to be used once and thrown out. Bricks, by contrast, are built to be taken apart and built again, and new bricks still fit bricks made since 1958.
Words to know
- polybutadiene: rubbery ingredient
- thermoplastics: meltable plastics
- tolerance: allowed error
- deformation: change of shape
- cavity: hollow space
