Silicone is a rubber-like nontoxic polymer, reusable and insulating, also used in medical and food objects.
We chose silicone because it is very much reusable. We do not hide the fact that producing it is not good for the environment, but considering reuse and proper disposal it is all in all convenient.
Silicone is a bit difficult to recycle. Some companies will do it for free in the US, just search the web. Silicone shouldn't be disposed with plastic. You can also recraft it using molds if you have the skills, search the web for DIY projects.