Thermoplastic is easy to use and can be reused indefinitely.
Use: Pour boiling water in a heat resistant bowl, then pour the granules into the water. Wait a few moments until they turn into a transparent mass.
Wait for the mass to cool down to approx. 60°C = 140°F, the plastic will become tacky and behave like hot glue: be careful not to burn yourself! You can now shape it with your hands into the desired shape. When the thermoplastic cools down to room temperature, it becomes a hard, white material again. You can submerge it in cold water to speed up the hardening.
It is also possible to use a heat gun to soften the thermoplastic, being very careful to not overheat it.
To re-use the thermoplastic or remove pieces from it, heat it up in hot water again. Residue can also be removed with white-spirit, but this is generally not necessary, as the plastic sticks to itself.
The granules are non-toxic, strong, reusable, light and biodegradable.