Green stuff is a room-temperature curing two-part epoxy putty sold in tape format.
Mixing equal parts of the yellow 'filler' and blue 'hardener' produces a sticky green putty that feels a lot like chewed bubble gum. Once mixed, it has a worklife of 90 minutes, allowing time for shaping and detailing, reaching 'ultimate hardness' after 24 hours. Altering the mix with more blue or yellow component will produce a faster/slower and harder/softer cure.
Keeping fingers and tools wet while working will make the sculpting and modelling process easier.
This set contains 12 inches of material --> 30 cm.