Not the same as the foam, but 2L Soda bottles work great. I used them last year to set a bunch of broccoli and peppers in a hot house structure for the winter. Everything came up nicely and was growing great. And then we had a huge storm and it knocked them all down even though I thought they were sheltered from the wind, but evidential they were not. And of course it happened on a Friday morning when we had left for the entire weekend this night before.
But the idea is cool, those bottles aren't going anywhere for years so why no use them for something worthwhile. The painting is just a cool touch. I know Shannon would have dragonflies all over them.
I wish we had done it this year again, but we just didn't have time with everything.