延展性（ductility and malleability），是物质的一种机械性质，表示材料在受力而产生破裂（fracture）之前，其塑性变形的能力。延展性是由延性、展性两个概念相近的机械性质合称。常见金属及许多合金均有延展性。

在材料科学中，延性（Ductility）是材料受到拉伸应力（tensile stress）变形时，特别被注目的材料能力。延性它主要表现在材料被拉伸成线条状时。展性（Malleability）是另外一个较相似的概念，但它表示为材料受到压缩应力（compressive stress）变形，而不破裂的能力。展性主要表现在材料受到锻造或轧制成薄板时。延性和展性两者间并不总是相关，如黄金具有良好的延性和展性，但铅仅仅有良好的展性而已。然而，通常上因这两个性质概念相近，常被称为延展性。

In materials science, ductility is a solid material's ability to deform under tensile stress; this is often characterized by the material's ability to be stretched into a wire. Malleability, a similar property, is a material's ability to deform under compressive stress; this is often characterized by the material's ability to form a thin sheet by hammering or rolling. Both of these mechanical properties are aspects of plasticity, the extent to which a solid material can be plastically deformed without fracture. Also, these material properties are dependent on temperature and pressure (investigated by Percy Williams Bridgman as part of his Nobel Prize-winning work on high pressures).