Why does bi color toothpaste never mix and always come out perfectly divided in 4 triangles?

Answer 1

From Wikipedia:

Striped toothpaste can be produced by including two different colored toothpastes in an unusual type of packaging. The collapsible tube has two tanks, one filled with each color paste (see figure). Squeezing the tube pushes the two pastes out the opening. The tube nozzle layers the pastes to produce a striped pattern. To keep the cost of packaging to a minimum, it is now common for tubes to be filled with striped paste (e.g. Aquafresh).[5] As the tube is squeezed, the stripes flow parallel to each other and do not mix. The patterned paste that gets dipensed is simply a narrower version of what is in the tube. Filling is done using a multi-nozzle filling head that dispenses a different colored stripe in each direction. To keep the stripes parallel to the axis of the tube, the head starts at the bottom and retracts as it fills, staying just above the level of the paste. Tubes with two compartments are generally reserved for toothpastes containing two formulas intended to react together and therefore kept isolated until dispensed (e.g. Colgate Simply White).

Answer 2

The bi-color toothpaste is formulated with a special type of stripe technology that helps to keep the two colors separate within the tube. As the toothpaste is dispensed, the pressure causes the two colors to come out in distinct stripes that do not mix together, resulting in the distinctive pattern of four triangles. This ensures that the toothpaste maintains its dual-color appearance until it is squeezed out.