Our last outdoor classroom teacher brought in a few sets of silicone cupcake liners. I didn’t think they would last long in the sun, but they are still going after two years! Although many have become sun bleached.
The kids use them all the time for sand cupcakes, or fill them with water. I almost picked up a set of shaped liners (a star and heart) but I didn’t end up with them because they were too flimsy.
I don’t know the brand of these, but they are pretty thick which is what has led to their durability outside. It is a good reminder for me that I should try things out, I may be surprised!