Ever wondered how they get the stripes on the toothpaste? Some people even avoid buying those stripy toothpastes just so they don't have to even think about this.

But it's easier than it seems. And no, there are not two separate compartments (cf the drawing below). The tube is filled with the carrier material, the actual toothpaste, which is usually white, to a certain level. Above that level, the tube is filled with the 'stripe' stuff, which is usually red, blue or green. Both materials are viscous enough so that they don't mix. Now the trick is to let these two substances out separate ways but at the same time. The toothpaste nozzle is not just a hole at the top of the tube. Instead, it is a longish pipe that reaches down the tube just ending at the filling level of the carrier material. The pipe has small holes in it further up closer to the nozzle. Pressing the tube will cause the carrier material to enter the outlet pipe and press the stripe stuff. The stripe material will enter the outlet pipe through the small holes, which is where the stripes are generated.

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