FIMO is a polymer clay
popular in both hobbyist
and professional art
communities. It has good tensile strength
and doesn't get sticky
or fluid (like many natural clays do) during modeling/sculpting.
FIMO does not require a kiln; it can be hardened (fired) by heat as low as 265°F (129°C), easily within range of a standard kitchen oven. The hardened product can be carved, filed, and painted, and is watertight.
FIMO is manufactured in dozens of colors including glow-in-the-dark and transparent and colors may be mixed via kneading.