How do we know whether we are dealing with PP or PET?
Polypropylene (PP) is dull and usually has a checkered profile. PP is manufactured in several standard colors, such as black, blue, white and yellow. Polyester (PET) shines and is often finished in the colors black or green. PP is easy to tear length-wise. With PET this is much more difficult. The specific gravity of PP is lower than that of PET. When it is placed in water, PP will continue to float. PET sinks to the bottom.