https://yle.fi/aihe/artikkeli/2019/05/02/kirkas-muovipullo-voi-kiertaa-ikuisesti-varilliset-pullot-eivat-kierra-samalla

https://www.youtube.com/watch?v=1P9syq3f6hQ

https://www.youtube.com/watch?v=ju_2NuK5O-E