The wax needs to be hard at room temperature so that it retains its shape.
But it can't be too brittle or it will be difficult to smooth out or add details to. It needs to fill the mold smoothly without bubbles.
Traditional bronze artisans used beeswax, although it is fairly soft. Today foundries use a vareity of formulas that blend petroleum-based
microcrystalline waxes with beeswax. Together, these mixes have the right combination of rigidity, smoothness, and a low enough melting point to be
safe and easy to work with.