Malleability is the ability of a material to undergo large permanent (plastic) deformation under compressive stress without cracking. Because the shaping operations that exploit malleability push and squeeze the metal rather than pull it, the governing stress is compressive.

Typical malleability-based processes all apply compression:

• Rolling — the metal is squeezed between rolls into sheet or plate.
• Forging — the workpiece is hammered or pressed into shape.
• Coining / pressing / stamping — the material is compressed in a die.

Metals such as gold, silver, aluminium and lead are highly malleable and can be beaten into very thin foils. The atomic reason is that these metals allow dislocations to glide easily along close-packed planes, so the crystal lattice can flow under compression rather than fracture.

It is important to distinguish malleability from the related but different property, ductility:

Therefore tensile stress is the answer for ductility, not malleability, so it is not correct here. Shear stress governs processes like shearing, punching and cutting, and fatigue stress refers to fluctuating cyclic loading that causes fatigue failure — neither defines malleability. The correct stress associated with malleability is compressive stress.