NILO is a binary alloy of nickel and iron, containing varying amounts of nickel. NILO is known as a controlled-expansion alloy. Controlled expansion alloys are characterized by a low expansion coefficient (in low and high temperature ranges), good ductility and toughness. These alloys also exhibit good mechanical properties.

Based on the nickel content of the alloy, the NILO alloys are named as NILO 36, NILO 42, NILO 48 and NILO alloy K. NILO 42 alloy consists of 42% nickel and is characterized by a low and constant co-efficient of thermal expansion from room temperature to about 300°C (570°F). NILO 42 alloy is available in the form of strip, wire, tube and sheet.