Malleability is the ability of a substance, usually a metal, to be deformed or molded into a different shape. Multiple factors can affect the malleability of a metal or alloy, but two fundamentally important factors are the strength of the metallic bond and the temperature.
The nature of metallic bond can be profoundly influence the ability of metal atoms to rearrange themselves. Strong metallic bond means that greater energy is required to move the metal atoms into different alignments. Weaker metallic bonds mean the metal atoms require less energy to shift positions and thus are more malleable.
The temperature of metal also affect malleability. For example at room temperature iron is not very malleable but when heated to higher temperatures become much more malleable and can be beaten with a hammer to make a thin sheet.