It is a single-phase alloy and can be cold rolled into sheets, unlike bell bronze.

As nickel and copper are mutually soluble in all proportions, it is a single-phase alloy.

Like other nickel/iron compositions, Invar is a solid solution; that is, it is a single-phase alloy, consisting of around 36% nickel and 64% iron.

This makes the metal harder and more brittle than a single-phase alloy, and also affects the way the metal responds to hardening by hammering and lathing, and greatly restricts the use of mechanised techniques of manufacture.

A few studies, however, suggested that despite the significance of stacking fault energy on the grain refinement at the early stages of straining, the steady-state grain size at large strains is mainly controlled by the homologous temperature in pure metals and by the interaction of solute atoms and dislocations in single-phase alloys.