Babbitt metal is most commonly used as a thin surface layer in a complex, multi-metal bearing. Its metal matrix composite structure is made up of small hard crystals dispersed in a softer metal matrix. The softer metal slightly erodes, creating paths for lubricant between the harder, high spots that provide the actual bearing surface. Tin is often used as the softer metal and friction causes the tin to melt and function as a lubricant, protecting the bearing from wear.