Ductility is a property presented by some materials, such as metal alloys or asphalt materials, which under the action of a force, can be plastically deformed "Plasticity (solid mechanics)") in a sustainable manner without breaking,[1]​ allowing wires or threads to be obtained from said material. Materials that have this property are called ductile. Non-ductile materials are classified as brittle. Although ductile materials can also break under adequate stress, this breakage only occurs after large deformations occur.

Some examples of very ductile materials are gold, silver, copper, bronze, and brass.

In other words, a material is ductile when the relationship between the longitudinal elongation produced by traction and the decrease in the transverse section "Section (geometry)") is very high.

In the field of metallurgy, ductile metal is understood to be that which undergoes large deformations before breaking, being the opposite of brittle metal, which breaks with hardly any deformation. Note that ductility is a phenomenon observable only in the plastic regime "Plasticity (solid mechanics)").

Ductile should not be confused with soft, since ductility is a property that as such manifests itself once the material is supporting a considerable force, sufficient to produce plasticization. That is, as long as the load is small, the deformation will also be small and in general the deformation will be elastic "Elasticity (solid mechanics)") and reversible), however, at a certain point the material yields and flows due to plasticization, deforming to a much greater extent than it had done until then but without breaking.

In a tensile test, ductile materials present a creep phase characterized by a large deformation with hardly any increase in load. From a technological point of view, apart from economic considerations, the use of ductile materials has advantages:

The ductility of a metal is assessed indirectly through resilience "Resilience (engineering)"). Ductility is the property of metals to form wires or threads of different thicknesses. Metals are characterized by their high ductility, which is explained because the atoms of metals are arranged in such a way that they can slide over each other and therefore can be stretched without breaking.

After a tension test, or tensile test, there are two measurements that provide us with information about the ductility of a material: the percentage of elongation and the percentage reduction in area.

Where L is the distance between the calibrated marks after sample failure.

where Af is the final cross-sectional area at the fracture surface.