I haven’t done them on plastic glasses myself, but here are a few previous comments from other readers that used plastic & shared the results. Hope this helps! :)

——

Amy M. SAYS:
I made these for my Twilight DVD release party and they were a huge hit! I made them the night before and they were still fine the next day (even living in humid Texas). I tried a hard plastic martini glass and it did not melt. I saved that one for last after the mixture cooled a little and I didn’t dip it as far down as the others. Even after the warnings I still burned myself (though not 3rd degree!) so take it slow and pay attention. I will make these again as everyone was so impressed by it! Thanks for such a cool idea!

———-

Toralinda SAYS:
I tried this both with plastic martini glasses and wine glasses.
The plastic martini glasses ended up melting a bit, though they were still usable.
The wine glasses looked excellent, and were easy to clean off (just soak them in hot water).

——-

twilight party planner SAYS:
This came out awesome! It was a great touch to our New Moon Premiere party and everyone loved it! I used plastic martini glasses, a few had a slightly melted edge, but still looked great. Even with the warnings of being burned, and being careful, still managed to get a second degree burn on my thumb, so heed the warnings!! It hurts, but it was worth it! A small sacrifice for a great party!