However, after I put them into the oven, the plastic didn't shrink nor harden. The transparent plastic changed colour to white. Another transparent plastic sort of melted. As I was doing it, I was also concerned if it was safe to melt these in the oven, which we also use for baking, as I could smell some light chemical fumes.
It didn't work. I need to check again, which is the correct plastic. I saw a packet of shrinkable plastic in Daiso, selling for RM5. I think I should get that instead.