When you squirt toothpaste how has it got neat coloured stripes on it? Surely in the tube it would all get mushed up?
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It does not all get mashed up in the tube. The tooth paste tube is filled with these stripes in the tube. When you squeze the toothpaste out it does not move that far in relation to each other so it still comes out striped. If you look close there is a tiny bit of unevenness where the toothpast have started to slowly mix but it is not much.
One solution is to have the toothpaste separated into quadrants containing alternating colors, and it will kinda look striped.
Other solution is to have an outer container and an inner one. The inner one contains the white paste, while the outer one contains the material with the stripe. The the stripe is added in the tube neck through small holes.
Ok, i understand that moderators will delete comments that say “Just google an image of a tube sliced apart, and it’ll immediately make sense” because it doesn’t explain in detail, but this is one of those “a picture is worth a thousand words” moments.
The tubes are packed axially along a center line, with the colors segregated in quadrants around that central axis. That way when you squeeze the tube, the paste ejects out from the centerline and the arrangement of colors in the tube is preserved. Also, see a picture and all of this will make sense.
The original invention by Marrafino ([https://patents.google.com/patent/US2789731](https://patents.google.com/patent/US2789731)) is shown in this German ELI5 style video: [https://youtu.be/Pius1MtUIrY](https://youtu.be/Pius1MtUIrY) – In short: there is an short inner plastic cylinder with fine holes behind the nozzle of the tube. In the factory you fill part of the tube around this cylinder with colored tooth paste and the rest with white one. If you press on the tube you force a thin stream of colored tooth paste through the holes onto the white center stream.
There are also more modern approaches that allow for multiple colors by adding additional reservoirs (e.g. [https://patents.google.com/patent/US4969767](https://patents.google.com/patent/US4969767)) and there seems also a system to fill the tube with stripes already present as shown in [https://beachpackagingdesign.com/boxvox/cutting-open-toothpaste-tubes](https://beachpackagingdesign.com/boxvox/cutting-open-toothpaste-tubes) – which requires some rheological trickery prevent the different colors from mixing.
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