Almost every complaint we hear about plastic cups is really a complaint about being sold the wrong resin. Here is the whole difference in four paragraphs.

What PET is

Polyethylene terephthalate is the glass-clear one: hard, glossy, genuinely transparent rather than merely see-through, and the reason a layered iced drink can look like a photograph on a counter.

It buys that clarity with rigidity. A hard grip crazes the wall white and the mark never goes away; a sharp cold shock against the metal of an ice bin can start a split at the rim and run it down the side.

What PP is

Polypropylene is faintly hazy — side by side against PET it reads very slightly milky — and in exchange it simply does not care. Squeeze it and it gives; let go and it returns. Drop it, ice it, hand it to a child.

Most buyers who insisted on glass-clarity were actually buying survivability and did not know there was a choice.

Choosing by where the cup lives

Poured, carried, set down, indoors — cocktail bars, cafe counters, display drinks — is PET country, and the clarity earns its keep.

Gripped, iced, dropped, carried across a concourse, handed to children — festivals, pools, stadiums, schools — is PP country, and clarity is the wrong thing to be optimising.

The one-second test

Squeeze the side wall between thumb and finger. Sharp crackle and a white stress line: PET. Silent give and no mark: PP.

Run it on whatever is in your storeroom right now. If the result surprises you, that is worth knowing before the next pallet.