Tin is a malleable, ductile, and highly crystalline silvery-white metal. Tin is malleable at ordinary temperatures but is brittle when it is cooled, due to the properties of two major allotropes, α and β tin. When a bar of tin is bent, a crackling sound known as the tin cry can be heard due to the twinning of the crystals.
Tin's chemical properties fall between those of metals and non-metals, just as the semiconductors silicon and germanium do. Tin has two allotropes at normal pressure and temperature: gray or α-tin and white or β-tin. Two more allotropes, γ and σ, exist at temperatures above 161 °C and pressures above several GPa.
Below 13.2 °C, tin exists in the gray α form, which has a diamond cubic crystal structure, similar to diamond, silicon or germanium. Gray tin has no metallic properties at all, is a dull-gray powdery material, and has few uses, other than a few specialized semiconductor applications.

Although the α-β transformation temperature is nominally 13.2 °C, impurities (e.g. Al, Zn, etc.) lower the transition temperature well below 0 °C, and upon addition of Sb or Bi the transformation may not occur at all. This conversion is known as tin disease or tin pest. Tin pest was a particular problem in northern Europe in the 18th century as organ pipes made of tin alloy would sometimes be affected during long cold winters. Some sources also say that during Napoleon's Russian campaign of 1812, the temperatures became so cold that the tin buttons on the soldiers' uniforms disintegrated, contributing to the defeat of the Grande Armée. The veracity of this story is debatable, because the transformation to gray tin often takes a reasonably long time.

Commercial grades of tin (99.8%) resist transformation because of the inhibiting effect of the small amounts of bismuth, antimony, lead, and silver present as impurities. Alloying elements such as copper, antimony, bismuth, cadmium, and silver increase its hardness. Tin tends rather easily to form hard, brittle intermetallic phases, which are often undesirable. It does not form wide solid solution ranges in other metals in general, and there are few elements that have appreciable solid solubility in tin. Simple eutectic systems, however, occur with bismuth, gallium, lead, thallium, and zinc.