New Constantan Ribbon/Constantan Flat Wire/Copper Nickel Alloys
Chemical Composition: 55.00 Copper, Ni44~45 Mn1~2
Electrical Resistivity: 0.48 ohm mm2/m
Shape: Strip/Sheet/Tape
Dimension: Thickness 0.03mm-3mm
Width: 6mm-150mm

Those are alloys of chemical composition copper + nickel with addition of manganese with a low resistivity (from 231.5 to 23.6 Ohm. Mm2/ft). The most known, CuNi40(also called Constantan) presents the advantage of a very low temperature coefficient.