All materials have certain physical properties which determine their fitness for specific purposes. Of first consideration in materials of construction is strength, or tenacity, which is the attraction between molecules of a material giving them the power to resist tearing apart. Next in consideration is the property of a material which allows a change of relative position of its molecules (which is change of shape), without destroying or seriously affecting tenacity.

Specific properties of materials are:

(1) Hardness, the property of resisting change of shape under pressure and separation into parts.

(2) Brittleness, associated with hardness, the property of resisting a change of the relative position of molecules, or liability to fracture without change of shape.

(3) Density, the weight of a unit volume usually compared with unit volume of water.

(4) Elasticity, the power of returning to the original shape upon removal of the force which has caused change of shape.

(5) Ductility, the property of metals allowing them to be drawn out, as in wire-making, without breaking.

(6) Malleability, similar to ductility, the property of metals allowing them to bend or be permanently distorted without rupture. Examples of this are rolling a metal into sheets or changing its form by hammering. Opposed to brittleness.

(7) Fusibility, the property of being liquefied by heat.

(8) Conductivity, the power to transmit molecular vibrations caused by heat or electricity.

(9) Contraction and expansion, the change of volume due to change of temperature.