According to this [1] German article by Golem, they're coated with wax, which should them give some basic resilience against wet weather conditions, which should be enough, since they're built as single-use devices.
You can make anything fly if all you need is a one off. FliteTest
has extensive experience in making stupid things go up. Here Ikea chair with cardboard wings https://www.youtube.com/watch?v=QlKC5qUS80o
[1] https://www.golem.de/news/origami-des-todes-ukraine-setzt-pa...