@Abdullah HDPE is used in bottles indeed. They are formed by straight chains of ilyethylene molecules of different chain lenght (molecular weight). By changing the average molecular weight, you can get vary the rigidity of the bottles. Also, since polymer molecules are straight, they pack better and prevent light from going through more efficiently, giving a more solid opaque white color (which can be mixed with pigments, like in the first three images you showed).
Low density polyethylene consist of straight and branched polyethylene molecules, which prevents them to pack tightly, being more flexible than HDPE and letting a bit more light to go through. That’s why plastic bags are “slightly” transarent.
PET is a different type of polymer, and is completely clear (can be coloured though). It’s also very shinny on the surface.