Standard LEGO bricks are primarily made from acrylonitrile butadiene styrene, commonly abbreviated as ABS.
LEGO began using ABS for its standard bricks in the 1960s, replacing cellulose acetate, an earlier plastic that could warp or shrink over time. ABS is valued because it is rigid, durable, moldable, and capable of producing the sharp edges and consistent dimensions needed for bricks to connect reliably.
The material is not identical across every LEGO product. Different elements can use other plastics when flexibility, transparency, softness, or special performance is required. Rubber-like parts, flexible hoses, transparent pieces, and electronic components may therefore have different formulations.
A common mix-up is treating ABS as the name of a LEGO product line. It is instead a widely used engineering thermoplastic. The important manufacturing challenge is precision: tiny dimensional variations can affect how firmly bricks connect, so LEGO controls molding tolerances very closely.