Since 1963, Lego pieces have been manufactured from a strong, resilient plastic known as acrylonitrile butadiene styrene (ABS). As of September 2008, Lego engineers use the NX CAD/CAM/CAE PLM software suite to model the elements. The software allows the parts to be optimised by way of mould flow and stress analysis. Prototype moulds are sometimes built before the design is committed to mass production. The ABS plastic is heated to 232 °C (450 °F) until it reaches a dough-like consistency. It is then injected into the moulds at pressures between 25 and 150 tonnes, and takes approximately 15 seconds to cool. The moulds are permitted a tolerance of up to twenty micrometres, to ensure the bricks remain connected. Human inspectors check the output of the moulds, to eliminate significant variations in colour or thickness. According to the Lego Group, about eighteen bricks out of every million fail to meet the standard required. Lego factories recycle all but about 1 percent of their plastic waste from the manufacturing process. If the plastic cannot be re-used in Lego bricks, it is processed and sold on to industries that can make use of it. Lego has a self-imposed 2030 deadline to find a more eco-friendly alternative to the ABS plastic it currently uses in its bricks.
Manufacturing of Lego bricks occurs at several locations around the world. Moulding is done in Billund, Denmark; Nyíregyháza, Hungary; Monterrey, Mexico and most recently in Jiaxing, China. Brick decorations and packaging are done at plants in Denmark, Hungary, Mexico and Kladno in the Czech Republic. The Lego Group estimates that in five decades it has produced 400 billion Lego blocks. Annual production of Lego bricks averages approximately 36 billion, or about 1140 elements per second. According to an article in BusinessWeek in 2006, Lego could be considered the world's No. 1 tire manufacturer; the factory produces about 306 million small rubber tires a year. The claim was reiterated in 2012.
In December 2012, the BBC's More or Less radio program asked the Open University's engineering department to determine "how many Lego bricks, stacked one on top of the other, it would take for the weight to destroy the bottom brick?" Using a hydraulic testing machine, the engineering department determined the average maximum force a 2×2 Lego brick can stand is 4,240 newtons; since an average 2×2 Lego brick has a mass of 1.152 grams (0.0406 oz), according to their calculations it would take a stack of 375,000 bricks to cause the bottom brick to collapse, which represents a stack 3,591 metres (11,781 ft) in height.
Private tests have shown several thousand assembly-disassembly cycles before the bricks begin to wear out, although Lego tests show fewer cycles.
In 2018, Lego announced that it will be using bio-derived polyethylene to make its botanical elements (parts such as leaves, bushes and trees).
