It is commonly known that one should not use a disposable plastic cup for kiddush. Rav Moshe Feinstein paskened not to because its value is almost worthless, insignificant, so it has no importance and cannot be considered a cup for kiddush. I have seen some people refuse to use one cup for kiddush but they would double it up with two cups saying that at that point it is already significant.

Rav Shaul Alter commented on this in a recent shiur, saying that we used to throw away disposable cups because they were cheap and insignificant. Now that the prices have gone up and it is expensive, people don't throw them out so quickly, some even wash them, and the cup now has significance and value. The disposable plastic cups, nowadays, because of the new taxes, would be considered usable for kiddush.

source: Kikar