We use Aerospace grade titanium on the spring/lock side liner. Titanium is the perfect material for that function and has all of the properties needed to perform the duties of a strong reliable locking liner system. The opposite side (non-lock side) is crafted from a 300 series stainless steel. This side of the knife functions as a handle frame stiffener and has a minimal mechanical function. The stainless steel is truly stainless. It will not rust and does not affect the overall performance, wear, or durability of the knife in any negative way.