This is an original 2x4 LEGO® Brick part# 3001 made of cellulose acetate between 1949-1970. It comes in its display clamshell packaging. Bricks are sold in used condition. 

After several fires at his wooden toy factory, Ole Kirk Christiansen shifted LEGO’s production to plastic toys. In 1947, he began making plastic bricks after acquiring an injection-molding machine, improving upon Kiddicraft's earlier English design by adding a tube system for better interlocking. LEGO introduced its first plastic bricks in 1949 using cellulose acetate, valued for its glossy finish and bright colors, which contributed to early brand success. However, cellulose acetate was unstable and led to warped bricks, prompting LEGO to switch to Acrylonitrile Butadiene Styrene, ABS, plastic in 1963, known for stability and color retention. The modern brick design, patented in 1958, improved strength, and by 1970, ABS fully replaced cellulose acetate, ensuring LEGO's durability and compatibility.